HTTP Message Signatures

1.1. Requirements Discussion

HTTP permits and sometimes requires intermediaries to transform messages in a variety of ways. This may result in a recipient receiving a message that is not bitwise equivalent to the message that was originally sent. In such a case, the recipient will be unable to verify a signature over the raw bytes of the sender's HTTP message, as verifying digital signatures or MACs requires both signer and verifier to have the exact same signature input. Since the exact raw bytes of the message cannot be relied upon as a reliable source of signature input, the signer and verifier must derive the signature input from their respective versions of the message, via a mechanism that is resilient to safe changes that do not alter the meaning of the message.¶

For a variety of reasons, it is impractical to strictly define what constitutes a safe change versus an unsafe one. Applications use HTTP in a wide variety of ways, and may disagree on whether a particular piece of information in a message (e.g., the body, or the Date header field) is relevant. Thus a general purpose solution must provide signers with some degree of control over which message components are signed.¶

HTTP applications may be running in environments that do not provide complete access to or control over HTTP messages (such as a web browser's JavaScript environment), or may be using libraries that abstract away the details of the protocol (such as the Java HTTPClient library). These applications need to be able to generate and verify signatures despite incomplete knowledge of the HTTP message.¶

1.2. HTTP Message Transformations

As mentioned earlier, HTTP explicitly permits and in some cases requires implementations to transform messages in a variety of ways. Implementations are required to tolerate many of these transformations. What follows is a non-normative and non-exhaustive list of transformations that may occur under HTTP, provided as context:¶

• Re-ordering of header fields with different header field names ([MESSAGING], Section 3.2.2).¶
• Combination of header fields with the same field name ([MESSAGING], Section 3.2.2).¶
• Removal of header fields listed in the Connection header field ([MESSAGING], Section 6.1).¶
• Addition of header fields that indicate control options ([MESSAGING], Section 6.1).¶
• Addition or removal of a transfer coding ([MESSAGING], Section 5.7.2).¶
• Addition of header fields such as Via ([MESSAGING], Section 5.7.1) and Forwarded ([RFC7239], Section 4).¶

1.3. Safe Transformations

Based on the definition of HTTP and the requirements described above, we can identify certain types of transformations that should not prevent signature verification, even when performed on message components covered by the signature. The following list describes those transformations:¶

• Combination of header fields with the same field name.¶
• Reordering of header fields with different names.¶
• Conversion between different versions of the HTTP protocol (e.g., HTTP/1.x to HTTP/2, or vice-versa).¶
• Changes in casing (e.g., "Origin" to "origin") of any case-insensitive components such as header field names, request URI scheme, or host.¶
• Addition or removal of leading or trailing whitespace to a header field value.¶
• Addition or removal of obs-folds.¶
• Changes to the request-target and Host header field that when applied together do not result in a change to the message's effective request URI, as defined in Section 5.5 of [MESSAGING].¶

Additionally, all changes to components not covered by the signature are considered safe.¶

1.4. Conventions and Terminology

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.¶

The terms "HTTP message", "HTTP request", "HTTP response", absolute-form, absolute-path, "effective request URI", "gateway", "header field", "intermediary", request-target, "sender", and "recipient" are used as defined in [MESSAGING].¶

The term "method" is to be interpreted as defined in Section 4 of [SEMANTICS].¶

For brevity, the term "signature" on its own is used in this document to refer to both digital signatures and keyed MACs. Similarly, the verb "sign" refers to the generation of either a digital signature or keyed MAC over a given input string. The qualified term "digital signature" refers specifically to the output of an asymmetric cryptographic signing operation.¶

In addition to those listed above, this document uses the following terms:¶

HTTP Message Signature:

A digital signature or keyed MAC that covers one or more portions of an HTTP message. Note that a given HTTP Message can contain multiple HTTP Message Signatures.¶

Signer:

The entity that is generating or has generated an HTTP Message Signature. Note that multiple entities can act as signers and apply separate HTTP Message Signatures to a given HTTP Message.¶

Verifier:

An entity that is verifying or has verified an HTTP Message Signature against an HTTP Message. Note that an HTTP Message Signature may be verified multiple times, potentially by different entities.¶

HTTP Message Component:

A portion of an HTTP message that is capable of being covered by an HTTP Message Signature.¶

HTTP Message Component Identifier:

A value that uniquely identifies a specific HTTP Message Component in respect to a particular HTTP Message Signature and the HTTP Message it applies to.¶

HTTP Message Component Value:

The value associated with a given component identifier within the context of a particular HTTP Message. Component values are derived from the HTTP Message and are usually subject to a canonicalization process.¶

Covered Components:

An ordered set of HTTP message component identifiers for fields (Section 2.1) and specialty components (Section 2.3) that indicates the set of message components covered by the signature, not including the @signature-params specialty identifier itself. The order of this set is preserved and communicated between the signer and verifier to facilitate reconstruction of the signature input.¶

Signature Input:

The sequence of bytes processed by the HTTP Message Signature algorithm to produce the HTTP Message Signature. The signature input is generated by the signer and verifier using the covered components set and the HTTP Message.¶

HTTP Message Signature Algorithm:

A cryptographic algorithm that describes the signing and verification process for the signature. When expressed explicitly, the value maps to a string defined in the HTTP Signature Algorithms Registry defined in this document.¶

Key Material:

The key material required to create or verify the signature. The key material is often identified with an explicit key identifier, allowing the signer to indicate to the verifier which key was used.¶

Creation Time:

A timestamp representing the point in time that the signature was generated, as asserted by the signer.¶

Expiration Time:

A timestamp representing the point in time at which the signature expires, as asserted by the signer. A signature's expiration time could be undefined, indicating that the signature does not expire from the perspective of the signer.¶

The term "Unix time" is defined by [POSIX.1], Section 4.16.¶

This document contains non-normative examples of partial and complete HTTP messages. Some examples use a single trailing backslash '' to indicate line wrapping for long values, as per [RFC8792]. The \ character and leading spaces on wrapped lines are not part of the value.¶

1.5. Application of HTTP Message Signatures

HTTP Message Signatures are designed to be a general-purpose security mechanism applicable in a wide variety of circumstances and applications. In order to properly and safely apply HTTP Message Signatures, an application or profile of this specification MUST specify all of the following items:¶

• The set of component identifiers (Section 2) that are expected and required. For example, an authorization protocol could mandate that the Authorization header be covered to protect the authorization credentials and mandate the signature parameters contain a created parameter, while an API expecting HTTP message bodies could require the Digest header to be present and covered.¶
• A means of retrieving the key material used to verify the signature. An application will usually use the keyid parameter of the signature parameters (Section 2.3.1) and define rules for resolving a key from there, though the appropriate key could be known from other means.¶
• A means of determining the signature algorithm used to verify the signature is appropriate for the key material. For example, the process could use the alg parameter of the signature parameters (Section 2.3.1) to state the algorithm explicitly, derive the algorithm from the key material, or use some pre-configured algorithm agreed upon by the signer and verifier.¶
• A means of determining that a given key and algorithm presented in the request are appropriate for the request being made. For example, a server expecting only ECDSA signatures should know to reject any RSA signatures, or a server expecting asymmetric cryptography should know to reject any symmetric cryptography.¶

An application using signatures also has to ensure that the verifier will have access to all required information to re-create the signature input string. For example, a server behind a reverse proxy would need to know the original request URI to make use of identifiers like @target-uri. Additionally, an application using signatures in responses would need to ensure that clients receiving signed responses have access to all the signed portions, including any portions of the request that were signed by the server.¶

The details of this kind of profiling are the purview of the application and outside the scope of this specification.¶

2.1. HTTP Fields

The component identifier for an HTTP field is the lowercased form of its field name. While HTTP field names are case-insensitive, implementations MUST use lowercased field names (e.g., content-type, date, etag) when using them as component identifiers.¶

Unless overridden by additional parameters and rules, the HTTP field value MUST be canonicalized with the following steps:¶

1. Create an ordered list of the field values of each instance of the field in the message, in the order that they occur (or will occur) in the message.¶
2. Strip leading and trailing whitespace from each item in the list.¶
3. Concatenate the list items together, with a comma "," and space " " between each item.¶

The resulting string is the canonicalized component value.¶

Host: www.example.com
Date: Tue, 07 Jun 2014 20:51:35 GMT
X-OWS-Header:   Leading and trailing whitespace.
X-Obs-Fold-Header: Obsolete
    line folding.
X-Empty-Header:
Cache-Control: max-age=60
Cache-Control:    must-revalidate
X-Dictionary:  a=1,    b=2;x=1;y=2,   c=(a   b   c)

2.2. Dictionary Structured Field Members

An individual member in the value of a Dictionary Structured Field is identified by using the parameter key on the component identifier for the field. The value of this parameter is a the key being identified, without any parameters present on that key in the original dictionary.¶

An individual member in the value of a Dictionary Structured Field is canonicalized by applying the serialization algorithm described in Section 4.1.2 of RFC8941 [RFC8941] on a Dictionary containing only that item.¶

X-Dictionary:  a=1, b=2;x=1;y=2, c=(a b c)

2.3. Specialty Components

Message components not found in an HTTP field can be included in the signature input by defining a component identifier and the canonicalization method for its component value.¶

To differentiate specialty component identifiers from HTTP fields, specialty component identifiers MUST start with the "at" @ character. This specification defines the following specialty component identifiers:¶

@signature-params

The signature metadata parameters for this signature. (Section 2.3.1)¶

@method

The method used for a request. (Section 2.3.2)¶

@target-uri

The full target URI for a request. (Section 2.3.3)¶

@authority

The authority of the target URI for a request. (Section 2.3.4)¶

@scheme

The scheme of the target URI for a request. (Section 2.3.5)¶

@request-target

The request target. (Section 2.3.6)¶

@path

The absolute path portion of the target URI for a request. (Section 2.3.7)¶

@query

The query portion of the target URI for a request. (Section 2.3.8)¶

@query-params

The parsed query parameters of the target URI for a request. (Section 2.3.9)¶

@status

The status code for a response. (Section 2.3.10).¶

@request-response

A signature from a request message that resulted in this response message. (Section 2.3.11)¶

Additional specialty component identifiers MAY be defined and registered in the HTTP Signatures Specialty Component Identifier Registry. (Section 6.3)¶

NOTE: '\' line wrapping per RFC 8792

("@target-uri" "@authority" "date" "cache-control" "x-empty-header" \
  "x-example");keyid="test-key-rsa-pss";alg="rsa-pss-sha512";\
  created=1618884475;expires=1618884775

POST /path?param=value HTTP/1.1
Host: www.example.com

"@method": POST

POST /path?param=value HTTP/1.1
Host: www.example.com

"@target-uri": https://www.example.com/path?param=value

POST /path?param=value HTTP/1.1
Host: www.example.com

"@authority": www.example.com

POST /path?param=value HTTP/1.1
Host: www.example.com

"@scheme": http

POST /path?param=value HTTP/1.1
Host: www.example.com

"@request-target": /path?param=value

GET https://www.example.com/path?param=value HTTP/1.1

"@request-target": https://www.example.com/path?param=value

CONNECT www.example.com:80 HTTP/1.1
Host: www.example.com

"@request-target": www.example.com:80

OPTIONS * HTTP/1.1
Host: www.example.com

"@request-target": *

POST /path?param=value HTTP/1.1
Host: www.example.com

"@path": /path

POST /path?param=value&foo=bar&baz=batman HTTP/1.1
Host: www.example.com

"@query": ?param=value&foo=bar&baz=batman

POST /path?queryString HTTP/1.1
Host: www.example.com

"@query": ?queryString

POST /path?param=value&foo=bar&baz=batman&qux= HTTP/1.1
Host: www.example.com

"@query-params";name="baz": batman
"@query-params";name="qux":
"@query-params";name="param": value

HTTP/1.1 200 OK
Date: Fri, 26 Mar 2010 00:05:00 GMT

"@status": 200

NOTE: '\' line wrapping per RFC 8792

POST /foo?param=value&pet=dog HTTP/1.1
Host: example.com
Date: Tue, 20 Apr 2021 02:07:55 GMT
Content-Type: application/json
Content-Length: 18
Signature-Input: sig1=("@authority" "content-type")\
  ;created=1618884475;keyid="test-key-rsa-pss"
Signature: sig1=:KuhJjsOKCiISnKHh2rln5ZNIrkRvue0DSu5rif3g7ckTbbX7C4\
  Jp3bcGmi8zZsFRURSQTcjbHdJtN8ZXlRptLOPGHkUa/3Qov79gBeqvHNUO4bhI27p\
  4WzD1bJDG9+6ml3gkrs7rOvMtROObPuc78A95fa4+skS/t2T7OjkfsHAm/enxf1fA\
  wkk15xj0n6kmriwZfgUlOqyff0XLwuH4XFvZ+ZTyxYNoo2+EfFg4NVfqtSJch2WDY\
  7n/qmhZOzMfyHlggWYFnDpyP27VrzQCQg8rM1Crp6MrwGLa94v6qP8pq0sQVq2DLt\
  4NJSoRRqXTvqlWIRnexmcKXjQFVz6YSA==:

{"hello": "world"}

HTTP/1.1 200 OK
Date: Tue, 20 Apr 2021 02:07:56 GMT
Content-Type: application/json
Content-Length: 62

{"busy": true, "message": "Your call is very important to us"}

NOTE: '\' line wrapping per RFC 8792

"content-type": application/json
"content-length": 62
"@status": 200
"@request-response";key="sig1": :KuhJjsOKCiISnKHh2rln5ZNIrkRvue0DSu\
  5rif3g7ckTbbX7C4Jp3bcGmi8zZsFRURSQTcjbHdJtN8ZXlRptLOPGHkUa/3Qov79\
  gBeqvHNUO4bhI27p4WzD1bJDG9+6ml3gkrs7rOvMtROObPuc78A95fa4+skS/t2T7\
  OjkfsHAm/enxf1fAwkk15xj0n6kmriwZfgUlOqyff0XLwuH4XFvZ+ZTyxYNoo2+Ef\
  Fg4NVfqtSJch2WDY7n/qmhZOzMfyHlggWYFnDpyP27VrzQCQg8rM1Crp6MrwGLa94\
  v6qP8pq0sQVq2DLt4NJSoRRqXTvqlWIRnexmcKXjQFVz6YSA==:
"@signature-params": ("content-type" "content-length" "@status" \
  "@request-response";key="sig1");created=1618884475\
  ;keyid="test-key-ecc-p256"

NOTE: '\' line wrapping per RFC 8792

HTTP/1.1 200 OK
Date: Tue, 20 Apr 2021 02:07:56 GMT
Content-Type: application/json
Content-Length: 62
Signature-Input: sig1=("content-type" "content-length" "@status" \
  "@request-response";key="sig1");created=1618884475\
  ;keyid="test-key-ecc-p256"
Signature: sig1=:crVqK54rxvdx0j7qnt2RL1oQSf+o21S/6Uk2hyFpoIfOT0q+Hv\
  msYAXUXzo0Wn8NFWh/OjWQOXHAQdVnTk87Pw==:

{"busy": true, "message": "Your call is very important to us"}

2.4. Creating the Signature Input String

The signature input is a US-ASCII string containing the canonicalized HTTP message components covered by the signature. To create the signature input string, the signer or verifier concatenates together entries for each identifier in the signature's covered components (including their parameters) using the following algorithm:¶

1. Let the output be an empty string.¶

2. For each message component item in the covered components set (in order):¶

   1. Append the component identifier for the covered component serialized according to the component-identifier rule.¶
   2. Append a single colon ":"¶
   3. Append a single space " "¶
   4. Append the covered component's canonicalized component value, as defined by the HTTP message component type. (Section 2.1 and Section 2.3)¶
   5. Append a single newline "\\n"¶

3. Append the signature parameters component (Section 2.3.1) as follows:¶

   1. Append the component identifier for the signature parameters serialized according to the component-identifier rule, i.e. "@signature-params"¶
   2. Append a single colon ":"¶
   3. Append a single space " "¶
   4. Append the signature parameters' canonicalized component value as defined in Section 2.3.1¶
4. Return the output string.¶

If covered components reference a component identifier that cannot be resolved to a component value in the message, the implementation MUST produce an error. Such situations are included but not limited to:¶

• The signer or verifier does not understand the component identifier.¶
• The component identifier identifies a field that is not present in the message or whose value is malformed.¶
• The component identifier is a Dictionary member identifier that references a field that is not present in the message, is not a Dictionary Structured Field, or whose value is malformed.¶
• The component identifier is a Dictionary member identifier that references a member that is not present in the field value, or whose value is malformed. E.g., the identifier is "x-dictionary";key="c" and the value of the x-dictionary header field is a=1, b=2¶

In the following non-normative example, the HTTP message being signed is the following request:¶

GET /foo HTTP/1.1
Host: example.org
Date: Tue, 20 Apr 2021 02:07:55 GMT
X-Example: Example header
        with some whitespace.
X-Empty-Header:
Cache-Control: max-age=60
Cache-Control: must-revalidate

The covered components consist of the @method, @path, and @authority specialty component identifiers followed by the Cache-Control, X-Empty-Header, X-Example HTTP headers, in order. The signature parameters consist of a creation timestamp is 1618884475 and the key identifier is test-key-rsa-pss. The signature input string for this message with these parameters is:¶

NOTE: '\' line wrapping per RFC 8792

"@method": GET
"@path": /foo
"@authority": example.org
"cache-control": max-age=60, must-revalidate
"x-empty-header":
"x-example": Example header with some whitespace.
"@signature-params": ("@method" "@path" "@authority" \
  "cache-control" "x-empty-header" "x-example");created=1618884475\
  ;keyid="test-key-rsa-pss"

3.1. Creating a Signature

In order to create a signature, a signer MUST follow the following algorithm:¶

1. The signer chooses an HTTP signature algorithm and key material for signing. The signer MUST choose key material that is appropriate for the signature's algorithm, and that conforms to any requirements defined by the algorithm, such as key size or format. The mechanism by which the signer chooses the algorithm and key material is out of scope for this document.¶
2. The signer sets the signature's creation time to the current time.¶
3. If applicable, the signer sets the signature's expiration time property to the time at which the signature is to expire.¶

4. The signer creates an ordered set of component identifiers representing the message components to be covered by the signature, and attaches signature metadata parameters to this set. The serialized value of this is later used as the value of the Signature-Input field as described in Section 4.1.¶

   • Once an order of covered components is chosen, the order MUST NOT change for the life of the signature.¶
   • Each covered component identifier MUST be either an HTTP field in the message Section 2.1 or a specialty component identifier listed in Section 2.3 or its associated registry.¶
   • Signers of a request SHOULD include some or all of the message control data in the covered components, such as the @method, @authority, @target-uri, or some combination thereof.¶
   • Signers SHOULD include the created signature metadata parameter to indicate when the signature was created.¶
   • The @signature-params specialty component identifier is not explicitly listed in the list of covered component identifiers, because it is required to always be present as the last line in the signature input. This ensures that a signature always covers its own metadata.¶
   • Further guidance on what to include in this set and in what order is out of scope for this document.¶
5. The signer creates the signature input string based on these signature parameters. (Section 2.4)¶
6. The signer signs the signature input with the chosen signing algorithm using the key material chosen by the signer. Several signing algorithms are defined in in Section 3.3.¶
7. The byte array output of the signature function is the HTTP message signature output value to be included in the Signature field as defined in Section 4.2.¶

For example, given the HTTP message and signature parameters in the example in Section 2.4, the example signature input string when signed with the test-key-rsa-pss key in Appendix B.1.2 gives the following message signature output value, encoded in Base64:¶

NOTE: '\' line wrapping per RFC 8792

P0wLUszWQjoi54udOtydf9IWTfNhy+r53jGFj9XZuP4uKwxyJo1RSHi+oEF1FuX6O29\
d+lbxwwBao1BAgadijW+7O/PyezlTnqAOVPWx9GlyntiCiHzC87qmSQjvu1CFyFuWSj\
dGa3qLYYlNm7pVaJFalQiKWnUaqfT4LyttaXyoyZW84jS8gyarxAiWI97mPXU+OVM64\
+HVBHmnEsS+lTeIsEQo36T3NFf2CujWARPQg53r58RmpZ+J9eKR2CD6IJQvacn5A4Ix\
5BUAVGqlyp8JYm+S/CWJi31PNUjRRCusCVRj05NrxABNFv3r5S9IXf2fYJK+eyW4AiG\
VMvMcOg==

3.2. Verifying a Signature

A verifier processes a signature and its associated signature input parameters in concert with each other.¶

In order to verify a signature, a verifier MUST follow the following algorithm:¶

1. Parse the Signature and Signature-Input fields and extract the signatures to be verified.¶

   1. If there is more than one signature value present, determine which signature should be processed for this message. If an applicable signature is not found, produce an error.¶
   2. If the chosen Signature value does not have a corresponding Signature-Input value, produce an error.¶
2. Parse the values of the chosen Signature-Input field to get the parameters for the signature to be verified.¶
3. Parse the value of the corresponding Signature field to get the byte array value of the signature to be verified.¶
4. Examine the signature parameters to confirm that the signature meets the requirements described in this document, as well as any additional requirements defined by the application such as which message components are required to be covered by the signature. (Section 3.2.1)¶
5. Determine the verification key material for this signature. If the key material is known through external means such as static configuration or external protocol negotiation, the verifier will use that. If the key is identified in the signature parameters, the verifier will dereference this to appropriate key material to use with the signature. The verifier has to determine the trustworthiness of the key material for the context in which the signature is presented. If a key is identified that the verifier does not know, does not trust for this request, or does not match something preconfigured, the verification MUST fail.¶

6. Determine the algorithm to apply for verification:¶

   1. If the algorithm is known through external means such as static configuration or external protocol negotiation, the verifier will use this algorithm.¶
   2. If the algorithm is explicitly stated in the signature parameters using a value from the HTTP Message Signatures registry, the verifier will use the referenced algorithm.¶
   3. If the algorithm can be determined from the keying material, such as through an algorithm field on the key value itself, the verifier will use this algorithm.¶
   4. If the algorithm is specified in more that one location, such as through static configuration and the algorithm signature parameter, or the algorithm signature parameter and from the key material itself, the resolved algorithms MUST be the same. If the algorithms are not the same, the verifier MUST vail the verification.¶
7. Use the received HTTP message and the signature's metadata to recreate the signature input, using the process described in Section 2.4. The value of the @signature-params input is the value of the SignatureInput field for this signature serialized according to the rules described in Section 2.3.1, not including the signature's label from the Signature-Input field.¶
8. If the key material is appropriate for the algorithm, apply the verification algorithm to the signature, recalculated signature input, signature parameters, key material, and algorithm. Several algorithms are defined in Section 3.3.¶
9. The results of the verification algorithm function are the final results of the signature verification.¶

If any of the above steps fail or produce an error, the signature validation fails.¶

3.3. Signature Algorithm Methods

HTTP Message signatures MAY use any cryptographic digital signature or MAC method that is appropriate for the key material, environment, and needs of the signer and verifier. All signatures are generated from and verified against the byte values of the signature input string defined in Section 2.4.¶

Each signature algorithm method takes as its input the signature input string as a set of byte values (I), the signing key material (Ks), and outputs the signature output as a set of byte values (S):¶

HTTP_SIGN (I, Ks)  ->  S

Each verification algorithm method takes as its input the recalculated signature input string as a set of byte values (I), the verification key material (Kv), and the presented signature to be verified as a set of byte values (S) and outputs the verification result (V) as a boolean:¶

HTTP_VERIFY (I, Kv, S) -> V

This section contains several common algorithm methods. The method to use can be communicated through the algorithm signature parameter defined in Section 2.3.1, by reference to the key material, or through mutual agreement between the signer and verifier.¶

4.1. The 'Signature-Input' HTTP Field

The Signature-Input HTTP field is a Dictionary Structured Field [RFC8941] containing the metadata for one or more message signatures generated from components within the HTTP message. Each member describes a single message signature. The member's name is an identifier that uniquely identifies the message signature within the context of the HTTP message. The member's value is the serialization of the covered components including all signature metadata parameters, using the serialization process defined in Section 2.3.1.¶

NOTE: '\' line wrapping per RFC 8792

Signature-Input: sig1=("@method" "@target-uri" "host" "date" \
  "cache-control" "x-empty-header" "x-example");created=1618884475\
  ;keyid="test-key-rsa-pss"

To facilitate signature validation, the Signature-Input field value MUST contain the same serialized value used in generating the signature input string's @signature-params value.¶

The signer MAY include the Signature-Input field as a trailer to facilitate signing a message after its content has been processed by the signer. However, since intermediaries are allowed to drop trailers as per [SEMANTICS], it is RECOMMENDED that the Signature-Input HTTP field be included only as a header to avoid signatures being inadvertently stripped from a message.¶

Multiple Signature-Input fields MAY be included in a single HTTP message. The signature labels MUST be unique across all field values.¶

4.2. The 'Signature' HTTP Field

The Signature HTTP field is a Dictionary Structured field [RFC8941] containing one or more message signatures generated from components within the HTTP message. Each member's name is a signature identifier that is present as a member name in the Signature-Input Structured field within the HTTP message. Each member's value is a Byte Sequence containing the signature value for the message signature identified by the member name. Any member in the Signature HTTP field that does not have a corresponding member in the HTTP message's Signature-Input HTTP field MUST be ignored.¶

NOTE: '\' line wrapping per RFC 8792

Signature: sig1=:P0wLUszWQjoi54udOtydf9IWTfNhy+r53jGFj9XZuP4uKwxyJo\
  1RSHi+oEF1FuX6O29d+lbxwwBao1BAgadijW+7O/PyezlTnqAOVPWx9GlyntiCiHz\
  C87qmSQjvu1CFyFuWSjdGa3qLYYlNm7pVaJFalQiKWnUaqfT4LyttaXyoyZW84jS8\
  gyarxAiWI97mPXU+OVM64+HVBHmnEsS+lTeIsEQo36T3NFf2CujWARPQg53r58Rmp\
  Z+J9eKR2CD6IJQvacn5A4Ix5BUAVGqlyp8JYm+S/CWJi31PNUjRRCusCVRj05NrxA\
  BNFv3r5S9IXf2fYJK+eyW4AiGVMvMcOg==:

The signer MAY include the Signature field as a trailer to facilitate signing a message after its content has been processed by the signer. However, since intermediaries are allowed to drop trailers as per [SEMANTICS], it is RECOMMENDED that the Signature-Input HTTP field be included only as a header to avoid signatures being inadvertently stripped from a message.¶

Multiple Signature fields MAY be included in a single HTTP message. The signature labels MUST be unique across all field values.¶

4.3. Multiple Signatures

Multiple distinct signatures MAY be included in a single message. Since Signature-Input and Signature are both defined as Dictionary Structured fields, they can be used to include multiple signatures within the same HTTP message by using distinct signature labels. For example, a signer may include multiple signatures signing the same message components with different keys or algorithms to support verifiers with different capabilities, or a reverse proxy may include information about the client in fields when forwarding the request to a service host, including a signature over the client's original signature values.¶

The following is a non-normative example of header fields a reverse proxy sets in addition to the examples in the previous sections.¶

NOTE: '\' line wrapping per RFC 8792

Forwarded: for=192.0.2.123
Signature-Input: sig1=("@method" "@path" "@authority" \
    "cache-control" "x-empty-header" "x-example")\
    ;created=1618884475;keyid="test-key-rsa-pss"
Signature: sig1=:P0wLUszWQjoi54udOtydf9IWTfNhy+r53jGFj9XZuP4uKwxyJo\
    1RSHi+oEF1FuX6O29d+lbxwwBao1BAgadijW+7O/PyezlTnqAOVPWx9GlyntiCi\
    HzC87qmSQjvu1CFyFuWSjdGa3qLYYlNm7pVaJFalQiKWnUaqfT4LyttaXyoyZW8\
    4jS8gyarxAiWI97mPXU+OVM64+HVBHmnEsS+lTeIsEQo36T3NFf2CujWARPQg53\
    r58RmpZ+J9eKR2CD6IJQvacn5A4Ix5BUAVGqlyp8JYm+S/CWJi31PNUjRRCusCV\
    Rj05NrxABNFv3r5S9IXf2fYJK+eyW4AiGVMvMcOg==:

The client's request includes a signature value under the label sig1, which the proxy signs in addition to the Forwarded header defined in [RFC7239]. Note that since the client's signature already covers the client's Signature-Input value for sig1, this value is transitively covered by the proxy's signature and need not be added explicitly. This results in a signature input string of:¶

NOTE: '\' line wrapping per RFC 8792

"signature";key="sig1": :P0wLUszWQjoi54udOtydf9IWTfNhy+r53jGFj9XZuP\
  4uKwxyJo1RSHi+oEF1FuX6O29d+lbxwwBao1BAgadijW+7O/PyezlTnqAOVPWx9Gl\
  yntiCiHzC87qmSQjvu1CFyFuWSjdGa3qLYYlNm7pVaJFalQiKWnUaqfT4LyttaXyo\
  yZW84jS8gyarxAiWI97mPXU+OVM64+HVBHmnEsS+lTeIsEQo36T3NFf2CujWARPQg\
  53r58RmpZ+J9eKR2CD6IJQvacn5A4Ix5BUAVGqlyp8JYm+S/CWJi31PNUjRRCusCV\
  Rj05NrxABNFv3r5S9IXf2fYJK+eyW4AiGVMvMcOg==:
"forwarded": for=192.0.2.123
"@signature-params": ("signature";key="sig1" "forwarded")\
  ;created=1618884480;keyid="test-key-rsa";alg="rsa-v1_5-sha256"

And a signature output value of:¶

NOTE: '\' line wrapping per RFC 8792

cjGvZwbsq9JwexP9TIvdLiivxqLINwp/ybAc19KOSQuLvtmMt3EnZxNiE+797dXK2cj\
PPUFqoZxO8WWx1SnKhAU9SiXBr99NTXRmA1qGBjqus/1Yxwr8keB8xzFt4inv3J3zP0\
k6TlLkRJstkVnNjuhRIUA/ZQCo8jDYAl4zWJJjppy6Gd1XSg03iUa0sju1yj6rcKbMA\
BBuzhUz4G0u1hZkIGbQprCnk/FOsqZHpwaWvY8P3hmcDHkNaavcokmq+3EBDCQTzgwL\
qfDmV0vLCXtDda6CNO2Zyum/pMGboCnQn/VkQ+j8kSydKoFg6EbVuGbrQijth6I0dDX\
2/HYcJg==

These values are added to the HTTP request message by the proxy. The original signature is included under the identifier sig1, and the reverse proxy's signature is included under the label proxy_sig. The proxy uses the key test-key-rsa to create its signature using the rsa-v1_5-sha256 signature algorithm, while the client's original signature was made using the key id of test-key-rsa-pss and an RSA PSS signature algorithm.¶

NOTE: '\' line wrapping per RFC 8792

Forwarded: for=192.0.2.123
Signature-Input: sig1=("@method" "@path" "@authority" \
    "cache-control" "x-empty-header" "x-example")\
    ;created=1618884475;keyid="test-key-rsa-pss", \
  proxy_sig=("signature";key="sig1" "forwarded")\
    ;created=1618884480;keyid="test-key-rsa";alg="rsa-v1_5-sha256"
Signature: sig1=:P0wLUszWQjoi54udOtydf9IWTfNhy+r53jGFj9XZuP4uKwxyJo\
    1RSHi+oEF1FuX6O29d+lbxwwBao1BAgadijW+7O/PyezlTnqAOVPWx9GlyntiCi\
    HzC87qmSQjvu1CFyFuWSjdGa3qLYYlNm7pVaJFalQiKWnUaqfT4LyttaXyoyZW8\
    4jS8gyarxAiWI97mPXU+OVM64+HVBHmnEsS+lTeIsEQo36T3NFf2CujWARPQg53\
    r58RmpZ+J9eKR2CD6IJQvacn5A4Ix5BUAVGqlyp8JYm+S/CWJi31PNUjRRCusCV\
    Rj05NrxABNFv3r5S9IXf2fYJK+eyW4AiGVMvMcOg==:, \
  proxy_sig=:cjGvZwbsq9JwexP9TIvdLiivxqLINwp/ybAc19KOSQuLvtmMt3EnZx\
    NiE+797dXK2cjPPUFqoZxO8WWx1SnKhAU9SiXBr99NTXRmA1qGBjqus/1Yxwr8k\
    eB8xzFt4inv3J3zP0k6TlLkRJstkVnNjuhRIUA/ZQCo8jDYAl4zWJJjppy6Gd1X\
    Sg03iUa0sju1yj6rcKbMABBuzhUz4G0u1hZkIGbQprCnk/FOsqZHpwaWvY8P3hm\
    cDHkNaavcokmq+3EBDCQTzgwLqfDmV0vLCXtDda6CNO2Zyum/pMGboCnQn/VkQ+\
    j8kSydKoFg6EbVuGbrQijth6I0dDX2/HYcJg==:

The proxy's signature and the client's original signature can be verified independently for the same message, based on the needs of the application. Since the proxy's signature covers the client signature, the backend service fronted by the proxy can trust that the proxy has validated the incoming signature.¶

5.1. The Accept-Signature Field

The Accept-Signature HTTP header field is a Dictionary Structured field [RFC8941] containing the metadata for one or more requested message signatures to be generated from message components of the target HTTP message. Each member describes a single message signature. The member's name is an identifier that uniquely identifies the requested message signature within the context of the target HTTP message. The member's value is the serialization of the desired covered components of the target message, including any allowed signature metadata parameters, using the serialization process defined in Section 2.3.1.¶

NOTE: '\' line wrapping per RFC 8792

Accept-Signature: sig1=("@method" "@target-uri" "host" "date" \
  "cache-control" "x-empty-header" "x-example")\
  ;keyid="test-key-rsa-pss"

The requested signature MAY include parameters, such as a desired algorithm or key identifier. These parameters MUST NOT include parameters that the signer is expected to generate, including the created and nonce parameters.¶

5.2. Processing an Accept-Signature

The receiver of an Accept-Signature field fulfills that header as follows:¶

1. Parse the field value as a Dictionary¶

2. For each member of the dictionary:¶

   1. The name of the member is the label of the output signature as specified in Section 4.1¶
   2. Parse the value of the member to obtain the set of covered component identifiers¶
   3. Process the requested parameters, such as the signing algorithm and key material. If any requested parameters cannot be fulfilled, or if the requested parameters conflict with those deemed appropriate to the target message, the process fails and returns an error.¶
   4. Select any additional parameters necessary for completing the signature¶
   5. Create the Signature-Input and Signature header values and associate them with the label¶
3. Optionally create any additional Signature-Input and Signature values, with unique labels not found in the Accept-Signature field¶
4. Combine all labeled Signature-Input and Signature values and attach both headers to the target message¶

Note that by this process, a signature applied to a target message MUST have the same label, MUST have the same set of covered component, and MAY have additional parameters. Also note that the target message MAY include additional signatures not specified by the Accept-Signature field.¶

6.1. HTTP Signature Algorithms Registry

This document defines HTTP Signature Algorithms, for which IANA is asked to create and maintain a new registry titled "HTTP Signature Algorithms". Initial values for this registry are given in Section 6.1.2. Future assignments and modifications to existing assignment are to be made through the Expert Review registration policy [RFC8126] and shall follow the template presented in Section 6.1.1.¶

Algorithms referenced by algorithm identifiers have to be fully defined with all parameters fixed. Algorithm identifiers in this registry are to be interpreted as whole string values and not as a combination of parts. That is to say, it is expected that implementors understand rsa-pss-sha512 as referring to one specific algorithm with its hash, mask, and salt values set as defined here. Implementors do not parse out the rsa, pss, and sha512 portions of the identifier to determine parameters of the signing algorithm from the string.¶

6.2. HTTP Signature Metadata Parameters Registry

This document defines the signature parameters structure, the values of which may have parameters containing metadata about a message signature. IANA is asked to create and maintain a new registry titled "HTTP Signature Metadata Parameters" to record and maintain the set of parameters defined for use with member values in the signature parameters structure. Initial values for this registry are given in Section 6.2.2. Future assignments and modifications to existing assignments are to be made through the Expert Review registration policy [RFC8126] and shall follow the template presented in Section 6.2.1.¶

6.3. HTTP Signature Specialty Component Identifiers Registry

This document defines a method for canonicalizing HTTP message components, including components that can be generated from the context of the HTTP message outside of the HTTP fields. These components are identified by a unique string, known as the component identifier. IANA is asked to create and maintain a new registry typed "HTTP Signature Specialty Component Identifiers" to record and maintain the set of non-field component identifiers and the methods to produce their associated component values. Initial values for this registry are given in Section 6.3.2. Future assignments and modifications to existing assignments are to be made through the Expert Review registration policy [RFC8126] and shall follow the template presented in Section 6.3.1.¶

B.1. Example Keys

This section provides cryptographic keys that are referenced in example signatures throughout this document. These keys MUST NOT be used for any purpose other than testing.¶

The key identifiers for each key are used throughout the examples in this specification. It is assumed for these examples that the signer and verifier can unambiguously dereference all key identifiers used here, and that the keys and algorithms used are appropriate for the context in which the signature is presented.¶

-----BEGIN RSA PUBLIC KEY-----
MIIBCgKCAQEAhAKYdtoeoy8zcAcR874L8cnZxKzAGwd7v36APp7Pv6Q2jdsPBRrw
WEBnez6d0UDKDwGbc6nxfEXAy5mbhgajzrw3MOEt8uA5txSKobBpKDeBLOsdJKFq
MGmXCQvEG7YemcxDTRPxAleIAgYYRjTSd/QBwVW9OwNFhekro3RtlinV0a75jfZg
kne/YiktSvLG34lw2zqXBDTC5NHROUqGTlML4PlNZS5Ri2U4aCNx2rUPRcKIlE0P
uKxI4T+HIaFpv8+rdV6eUgOrB2xeI1dSFFn/nnv5OoZJEIB+VmuKn3DCUcCZSFlQ
PSXSfBDiUGhwOw76WuSSsf1D4b/vLoJ10wIDAQAB
-----END RSA PUBLIC KEY-----

-----BEGIN RSA PRIVATE KEY-----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-----END RSA PRIVATE KEY-----

-----BEGIN PUBLIC KEY-----
MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAr4tmm3r20Wd/PbqvP1s2
+QEtvpuRaV8Yq40gjUR8y2Rjxa6dpG2GXHbPfvMs8ct+Lh1GH45x28Rw3Ry53mm+
oAXjyQ86OnDkZ5N8lYbggD4O3w6M6pAvLkhk95AndTrifbIFPNU8PPMO7OyrFAHq
gDsznjPFmTOtCEcN2Z1FpWgchwuYLPL+Wokqltd11nqqzi+bJ9cvSKADYdUAAN5W
Utzdpiy6LbTgSxP7ociU4Tn0g5I6aDZJ7A8Lzo0KSyZYoA485mqcO0GVAdVw9lq4
aOT9v6d+nb4bnNkQVklLQ3fVAvJm+xdDOp9LCNCN48V2pnDOkFV6+U9nV5oyc6XI
2wIDAQAB
-----END PUBLIC KEY-----

-----BEGIN PRIVATE KEY-----
MIIEvgIBADALBgkqhkiG9w0BAQoEggSqMIIEpgIBAAKCAQEAr4tmm3r20Wd/Pbqv
P1s2+QEtvpuRaV8Yq40gjUR8y2Rjxa6dpG2GXHbPfvMs8ct+Lh1GH45x28Rw3Ry5
3mm+oAXjyQ86OnDkZ5N8lYbggD4O3w6M6pAvLkhk95AndTrifbIFPNU8PPMO7Oyr
FAHqgDsznjPFmTOtCEcN2Z1FpWgchwuYLPL+Wokqltd11nqqzi+bJ9cvSKADYdUA
AN5WUtzdpiy6LbTgSxP7ociU4Tn0g5I6aDZJ7A8Lzo0KSyZYoA485mqcO0GVAdVw
9lq4aOT9v6d+nb4bnNkQVklLQ3fVAvJm+xdDOp9LCNCN48V2pnDOkFV6+U9nV5oy
c6XI2wIDAQABAoIBAQCUB8ip+kJiiZVKF8AqfB/aUP0jTAqOQewK1kKJ/iQCXBCq
pbo360gvdt05H5VZ/RDVkEgO2k73VSsbulqezKs8RFs2tEmU+JgTI9MeQJPWcP6X
aKy6LIYs0E2cWgp8GADgoBs8llBq0UhX0KffglIeek3n7Z6Gt4YFge2TAcW2WbN4
XfK7lupFyo6HHyWRiYHMMARQXLJeOSdTn5aMBP0PO4bQyk5ORxTUSeOciPJUFktQ
HkvGbym7KryEfwH8Tks0L7WhzyP60PL3xS9FNOJi9m+zztwYIXGDQuKM2GDsITeD
2mI2oHoPMyAD0wdI7BwSVW18p1h+jgfc4dlexKYRAoGBAOVfuiEiOchGghV5vn5N
RDNscAFnpHj1QgMr6/UG05RTgmcLfVsI1I4bSkbrIuVKviGGf7atlkROALOG/xRx
DLadgBEeNyHL5lz6ihQaFJLVQ0u3U4SB67J0YtVO3R6lXcIjBDHuY8SjYJ7Ci6Z6
vuDcoaEujnlrtUhaMxvSfcUJAoGBAMPsCHXte1uWNAqYad2WdLjPDlKtQJK1diCm
rqmB2g8QE99hDOHItjDBEdpyFBKOIP+NpVtM2KLhRajjcL9Ph8jrID6XUqikQuVi
4J9FV2m42jXMuioTT13idAILanYg8D3idvy/3isDVkON0X3UAVKrgMEne0hJpkPL
FYqgetvDAoGBAKLQ6JZMbSe0pPIJkSamQhsehgL5Rs51iX4m1z7+sYFAJfhvN3Q/
OGIHDRp6HjMUcxHpHw7U+S1TETxePwKLnLKj6hw8jnX2/nZRgWHzgVcY+sPsReRx
NJVf+Cfh6yOtznfX00p+JWOXdSY8glSSHJwRAMog+hFGW1AYdt7w80XBAoGBAImR
NUugqapgaEA8TrFxkJmngXYaAqpA0iYRA7kv3S4QavPBUGtFJHBNULzitydkNtVZ
3w6hgce0h9YThTo/nKc+OZDZbgfN9s7cQ75x0PQCAO4fx2P91Q+mDzDUVTeG30mE
t2m3S0dGe47JiJxifV9P3wNBNrZGSIF3mrORBVNDAoGBAI0QKn2Iv7Sgo4T/XjND
dl2kZTXqGAk8dOhpUiw/HdM3OGWbhHj2NdCzBliOmPyQtAr770GITWvbAI+IRYyF
S7Fnk6ZVVVHsxjtaHy1uJGFlaZzKR4AGNaUTOJMs6NadzCmGPAxNQQOCqoUjn4XR
rOjr9w349JooGXhOxbu8nOxX
-----END PRIVATE KEY-----

-----BEGIN EC PRIVATE KEY-----
MHcCAQEEIFKbhfNZfpDsW43+0+JjUr9K+bTeuxopu653+hBaXGA7oAoGCCqGSM49
AwEHoUQDQgAEqIVYZVLCrPZHGHjP17CTW0/+D9Lfw0EkjqF7xB4FivAxzic30tMM
4GF+hR6Dxh71Z50VGGdldkkDXZCnTNnoXQ==
-----END EC PRIVATE KEY-----

-----BEGIN PUBLIC KEY-----
MFkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAEqIVYZVLCrPZHGHjP17CTW0/+D9Lf
w0EkjqF7xB4FivAxzic30tMM4GF+hR6Dxh71Z50VGGdldkkDXZCnTNnoXQ==
-----END PUBLIC KEY-----

NOTE: '\' line wrapping per RFC 8792

uzvJfB4u3N0Jy4T7NZ75MDVcr8zSTInedJtkgcu46YW4XByzNJjxBdtjUkdJPBt\
  bmHhIDi6pcl8jsasjlTMtDQ==

B.2. Test Cases

This section provides non-normative examples that may be used as test cases to validate implementation correctness. These examples are based on the following HTTP messages:¶

For requests, this test-request message is used:¶

POST /foo?param=value&pet=dog HTTP/1.1
Host: example.com
Date: Tue, 20 Apr 2021 02:07:55 GMT
Content-Type: application/json
Digest: SHA-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=
Content-Length: 18

{"hello": "world"}

For responses, this test-response message is used:¶

HTTP/1.1 200 OK
Date: Tue, 20 Apr 2021 02:07:56 GMT
Content-Type: application/json
Digest: SHA-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=
Content-Length: 18

{"hello": "world"}

NOTE: '\' line wrapping per RFC 8792

"@signature-params": ();created=1618884475\
  ;keyid="test-key-rsa-pss";alg="rsa-pss-sha512"

NOTE: '\' line wrapping per RFC 8792

Signature-Input: sig1=();created=1618884475\
  ;keyid="test-key-rsa-pss";alg="rsa-pss-sha512"
Signature: sig1=:HWP69ZNiom9Obu1KIdqPPcu/C1a5ZUMBbqS/xwJECV8bhIQVmE\
  AAAzz8LQPvtP1iFSxxluDO1KE9b8L+O64LEOvhwYdDctV5+E39Jy1eJiD7nYREBgx\
  TpdUfzTO+Trath0vZdTylFlxK4H3l3s/cuFhnOCxmFYgEa+cw+StBRgY1JtafSFwN\
  cZgLxVwialuH5VnqJS4JN8PHD91XLfkjMscTo4jmVMpFd3iLVe0hqVFl7MDt6TMkw\
  IyVFnEZ7B/VIQofdShO+C/7MuupCSLVjQz5xA+Zs6Hw+W9ESD/6BuGs6LF1TcKLxW\
  +5K+2zvDY/Cia34HNpRW5io7Iv9/b7iQ==:

NOTE: '\' line wrapping per RFC 8792

"@authority": example.com
"content-type": application/json
"@signature-params": ("@authority" "content-type")\
  ;created=1618884475;keyid="test-key-rsa-pss"

NOTE: '\' line wrapping per RFC 8792

Signature-Input: sig1=("@authority" "content-type")\
  ;created=1618884475;keyid="test-key-rsa-pss"
Signature: sig1=:ik+OtGmM/kFqENDf9Plm8AmPtqtC7C9a+zYSaxr58b/E6h81gh\
  JS3PcH+m1asiMp8yvccnO/RfaexnqanVB3C72WRNZN7skPTJmUVmoIeqZncdP2mlf\
  xlLP6UbkrgYsk91NS6nwkKC6RRgLhBFqzP42oq8D2336OiQPDAo/04SxZt4Wx9nDG\
  uy2SfZJUhsJqZyEWRk4204x7YEB3VxDAAlVgGt8ewilWbIKKTOKp3ymUeQIwptqYw\
  v0l8mN404PPzRBTpB7+HpClyK4CNp+SVv46+6sHMfJU4taz10s/NoYRmYCGXyadzY\
  YDj0BYnFdERB6NblI/AOWFGl5Axhhmjg==:

NOTE: '\' line wrapping per RFC 8792

"date": Tue, 20 Apr 2021 02:07:56 GMT
"@method": POST
"@path": /foo
"@query": ?param=value&pet=dog
"@authority": example.com
"content-type": application/json
"digest": SHA-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=
"content-length": 18
"@signature-params": ("date" "@method" "@path" "@query" \
  "@authority" "content-type" "digest" "content-length")\
  ;created=1618884475;keyid="test-key-rsa-pss"

NOTE: '\' line wrapping per RFC 8792

Signature-Input: sig1=("date" "@method" "@path" "@query" \
  "@authority" "content-type" "digest" "content-length")\
  ;created=1618884475;keyid="test-key-rsa-pss"
Signature: sig1=:JuJnJMFGD4HMysAGsfOY6N5ZTZUknsQUdClNG51VezDgPUOW03\
  QMe74vbIdndKwW1BBrHOHR3NzKGYZJ7X3ur23FMCdANe4VmKb3Rc1Q/5YxOO8p7Ko\
  yfVa4uUcMk5jB9KAn1M1MbgBnqwZkRWsbv8ocCqrnD85Kavr73lx51k1/gU8w673W\
  T/oBtxPtAn1eFjUyIKyA+XD7kYph82I+ahvm0pSgDPagu917SlqUjeaQaNnlZzO03\
  Iy1RZ5XpgbNeDLCqSLuZFVID80EohC2CQ1cL5svjslrlCNstd2JCLmhjL7xV3NYXe\
  rLim4bqUQGRgDwNJRnqobpS6C1NBns/Q==:

NOTE: '\' line wrapping per RFC 8792

"content-type": application/json
"digest": SHA-256=X48E9qOokqqrvdts8nOJRJN3OWDUoyWxBf7kbu9DBPE=
"content-length": 18
"@signature-params": ("content-type" "digest" "content-length")\
  ;created=1618884475;keyid="test-key-ecc-p256"

NOTE: '\' line wrapping per RFC 8792

Signature-Input: sig1=("content-type" "digest" "content-length")\
  ;created=1618884475;keyid="test-key-ecc-p256"
Signature: sig1=:n8RKXkj0iseWDmC6PNSQ1GX2R9650v+lhbb6rTGoSrSSx18zmn\
  6fPOtBx48/WffYLO0n1RHHf9scvNGAgGq52Q==:

NOTE: '\' line wrapping per RFC 8792

"@authority": example.com
"date": Tue, 20 Apr 2021 02:07:55 GMT
"content-type": application/json
"@signature-params": ("@authority" "date" "content-type")\
  ;created=1618884475;keyid="test-shared-secret"

NOTE: '\' line wrapping per RFC 8792

Signature-Input: sig1=("@authority" "date" "content-type")\
  ;created=1618884475;keyid="test-shared-secret"
Signature: sig1=:fN3AMNGbx0V/cIEKkZOvLOoC3InI+lM2+gTv22x3ia8=:

B.3. TLS-Terminating Proxies

In this example, there is a TLS-terminating reverse proxy sitting in front of the resource. The client does not sign the request but instead uses mutual TLS to make its call. The terminating proxy validates the TLS stream and injects a Client-Cert header according to [I-D.ietf-httpbis-client-cert-field]. By signing this header field, a reverse proxy can not only attest to its own validation of the initial request but also authenticate itself to the backend system independently of the client's actions. The client makes the following request to the TLS terminating proxy using mutual TLS:¶

POST /foo?Param=value&pet=Dog HTTP/1.1
Host: example.com
Date: Tue, 20 Apr 2021 02:07:55 GMT
Content-Type: application/json
Content-Length: 18

{"hello": "world"}

The proxy processes the TLS connection and extracts the client's TLS certificate to a Client-Cert header field and passes it along to the internal service hosted at service.internal.example. This results in the following unsigned request:¶

NOTE: '\' line wrapping per RFC 8792

POST /foo?Param=value&pet=Dog HTTP/1.1
Host: service.internal.example
Date: Tue, 20 Apr 2021 02:07:55 GMT
Content-Type: application/json
Content-Length: 18
Client-Cert: :MIIBqDCCAU6gAwIBAgIBBzAKBggqhkjOPQQDAjA6MRswGQYDVQQKD\
  BJMZXQncyBBdXRoZW50aWNhdGUxGzAZBgNVBAMMEkxBIEludGVybWVkaWF0ZSBDQT\
  AeFw0yMDAxMTQyMjU1MzNaFw0yMTAxMjMyMjU1MzNaMA0xCzAJBgNVBAMMAkJDMFk\
  wEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAE8YnXXfaUgmnMtOXU/IncWalRhebrXmck\
  C8vdgJ1p5Be5F/3YC8OthxM4+k1M6aEAEFcGzkJiNy6J84y7uzo9M6NyMHAwCQYDV\
  R0TBAIwADAfBgNVHSMEGDAWgBRm3WjLa38lbEYCuiCPct0ZaSED2DAOBgNVHQ8BAf\
  8EBAMCBsAwEwYDVR0lBAwwCgYIKwYBBQUHAwIwHQYDVR0RAQH/BBMwEYEPYmRjQGV\
  4YW1wbGUuY29tMAoGCCqGSM49BAMCA0gAMEUCIBHda/r1vaL6G3VliL4/Di6YK0Q6\
  bMjeSkC3dFCOOB8TAiEAx/kHSB4urmiZ0NX5r5XarmPk0wmuydBVoU4hBVZ1yhk=:

{"hello": "world"}

Without a signature, the internal service would need to trust that the incoming connection has the right information. By signing the Client-Cert header and other portions of the internal request, the internal service can be assured that the correct party, the trusted proxy, has processed the request and presented it to the correct service. The proxy's signature input consists of the following:¶

NOTE: '\' line wrapping per RFC 8792

"@path": /foo
"@query": Param=value&pet=Dog
"@method": POST
"@authority": service.internal.example
"client-cert": :MIIBqDCCAU6gAwIBAgIBBzAKBggqhkjOPQQDAjA6MRswGQYDVQQ\
  KDBJMZXQncyBBdXRoZW50aWNhdGUxGzAZBgNVBAMMEkxBIEludGVybWVkaWF0ZSBD\
  QTAeFw0yMDAxMTQyMjU1MzNaFw0yMTAxMjMyMjU1MzNaMA0xCzAJBgNVBAMMAkJDM\
  FkwEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAE8YnXXfaUgmnMtOXU/IncWalRhebrXm\
  ckC8vdgJ1p5Be5F/3YC8OthxM4+k1M6aEAEFcGzkJiNy6J84y7uzo9M6NyMHAwCQY\
  DVR0TBAIwADAfBgNVHSMEGDAWgBRm3WjLa38lbEYCuiCPct0ZaSED2DAOBgNVHQ8B\
  Af8EBAMCBsAwEwYDVR0lBAwwCgYIKwYBBQUHAwIwHQYDVR0RAQH/BBMwEYEPYmRjQ\
  GV4YW1wbGUuY29tMAoGCCqGSM49BAMCA0gAMEUCIBHda/r1vaL6G3VliL4/Di6YK0\
  Q6bMjeSkC3dFCOOB8TAiEAx/kHSB4urmiZ0NX5r5XarmPk0wmuydBVoU4hBVZ1yhk=:
"@signature-params": ("@path" "@query" "@method" "@authority" \
  "client-cert");created=1618884475;keyid="test-key-ecc-p256"

This results in the following signature:¶

NOTE: '\' line wrapping per RFC 8792

5gudRjXaHrAYbEaQUOoY9TuvqWOdPcspkp7YyKCB0XhyAG9cB715hucPPanEK0OVyiN\
LJqcoq2Yn1DPWQcnbog==

Which results in the following signed request sent from the proxy to the internal service:¶

NOTE: '\' line wrapping per RFC 8792

POST /foo?Param=value&pet=Dog HTTP/1.1
Host: service.internal.example
Date: Tue, 20 Apr 2021 02:07:55 GMT
Content-Type: application/json
Content-Length: 18
Client-Cert: :MIIBqDCCAU6gAwIBAgIBBzAKBggqhkjOPQQDAjA6MRswGQYDVQQKD\
  BJMZXQncyBBdXRoZW50aWNhdGUxGzAZBgNVBAMMEkxBIEludGVybWVkaWF0ZSBDQT\
  AeFw0yMDAxMTQyMjU1MzNaFw0yMTAxMjMyMjU1MzNaMA0xCzAJBgNVBAMMAkJDMFk\
  wEwYHKoZIzj0CAQYIKoZIzj0DAQcDQgAE8YnXXfaUgmnMtOXU/IncWalRhebrXmck\
  C8vdgJ1p5Be5F/3YC8OthxM4+k1M6aEAEFcGzkJiNy6J84y7uzo9M6NyMHAwCQYDV\
  R0TBAIwADAfBgNVHSMEGDAWgBRm3WjLa38lbEYCuiCPct0ZaSED2DAOBgNVHQ8BAf\
  8EBAMCBsAwEwYDVR0lBAwwCgYIKwYBBQUHAwIwHQYDVR0RAQH/BBMwEYEPYmRjQGV\
  4YW1wbGUuY29tMAoGCCqGSM49BAMCA0gAMEUCIBHda/r1vaL6G3VliL4/Di6YK0Q6\
  bMjeSkC3dFCOOB8TAiEAx/kHSB4urmiZ0NX5r5XarmPk0wmuydBVoU4hBVZ1yhk=:
Signature-Input: ttrp=("@path" "@query" "@method" "@authority" \
  "client-cert");created=1618884475;keyid="test-key-ecc-p256"
Signature: ttrp=:5gudRjXaHrAYbEaQUOoY9TuvqWOdPcspkp7YyKCB0XhyAG9cB7\
  15hucPPanEK0OVyiNLJqcoq2Yn1DPWQcnbog==:

{"hello": "world"}

The internal service can validate the proxy's signature and therefore be able to trust that the client's certificate has been appropriately processed.¶