The Proxy-Status HTTP Response Header Field
draft-ietf-httpbis-proxy-status-05
HTTP M. Nottingham
Internet-Draft Fastly
Intended status: Standards Track P. Sikora
Expires: 29 October 2021 Google
27 April 2021
The Proxy-Status HTTP Response Header Field
draft-ietf-httpbis-proxy-status-05
Abstract
This document defines the Proxy-Status HTTP field to convey the
details of intermediary response handling, including generated
errors.
Note to Readers
_RFC EDITOR: please remove this section before publication_
Discussion of this draft takes place on the HTTP working group
mailing list (ietf-http-wg@w3.org), which is archived at
https://lists.w3.org/Archives/Public/ietf-http-wg/
(https://lists.w3.org/Archives/Public/ietf-http-wg/).
Working Group information can be found at https://httpwg.org/
(https://httpwg.org/); source code and issues list for this draft can
be found at https://github.com/httpwg/http-extensions/labels/proxy-
status (https://github.com/httpwg/http-extensions/labels/proxy-
status).
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on 29 October 2021.
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Copyright Notice
Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Notational Conventions . . . . . . . . . . . . . . . . . 4
2. The Proxy-Status HTTP Field . . . . . . . . . . . . . . . . . 4
2.1. Proxy-Status Parameters . . . . . . . . . . . . . . . . . 5
2.1.1. error . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1.2. next-hop . . . . . . . . . . . . . . . . . . . . . . 6
2.1.3. next-protocol . . . . . . . . . . . . . . . . . . . . 7
2.1.4. received-status . . . . . . . . . . . . . . . . . . . 7
2.1.5. details . . . . . . . . . . . . . . . . . . . . . . . 7
2.2. Defining New Proxy-Status Parameters . . . . . . . . . . 7
2.3. Proxy Error Types . . . . . . . . . . . . . . . . . . . . 8
2.3.1. DNS Timeout . . . . . . . . . . . . . . . . . . . . . 8
2.3.2. DNS Error . . . . . . . . . . . . . . . . . . . . . . 8
2.3.3. Destination Not Found . . . . . . . . . . . . . . . . 9
2.3.4. Destination Unavailable . . . . . . . . . . . . . . . 9
2.3.5. Destination IP Prohibited . . . . . . . . . . . . . . 9
2.3.6. Destination IP Unroutable . . . . . . . . . . . . . . 10
2.3.7. Connection Refused . . . . . . . . . . . . . . . . . 10
2.3.8. Connection Terminated . . . . . . . . . . . . . . . . 10
2.3.9. Connection Timeout . . . . . . . . . . . . . . . . . 10
2.3.10. Connection Read Timeout . . . . . . . . . . . . . . . 11
2.3.11. Connection Write Timeout . . . . . . . . . . . . . . 11
2.3.12. Connection Limit Reached . . . . . . . . . . . . . . 11
2.3.13. TLS Protocol Error . . . . . . . . . . . . . . . . . 11
2.3.14. TLS Certificate Error . . . . . . . . . . . . . . . . 12
2.3.15. TLS Alert Received . . . . . . . . . . . . . . . . . 12
2.3.16. HTTP Request Error . . . . . . . . . . . . . . . . . 13
2.3.17. HTTP Request Denied . . . . . . . . . . . . . . . . . 13
2.3.18. HTTP Incomplete Response . . . . . . . . . . . . . . 13
2.3.19. HTTP Response Header Section Too Large . . . . . . . 14
2.3.20. HTTP Response Header Too Large . . . . . . . . . . . 14
2.3.21. HTTP Response Body Too Large . . . . . . . . . . . . 14
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2.3.22. HTTP Response Trailer Section Too Large . . . . . . . 15
2.3.23. HTTP Response Trailer Too Large . . . . . . . . . . . 15
2.3.24. HTTP Response Transfer-Coding Error . . . . . . . . . 16
2.3.25. HTTP Response Content-Coding Error . . . . . . . . . 16
2.3.26. HTTP Response Timeout . . . . . . . . . . . . . . . . 16
2.3.27. HTTP Upgrade Failed . . . . . . . . . . . . . . . . . 17
2.3.28. HTTP Protocol Error . . . . . . . . . . . . . . . . . 17
2.3.29. Proxy Internal Response . . . . . . . . . . . . . . . 17
2.3.30. Proxy Internal Error . . . . . . . . . . . . . . . . 17
2.3.31. Proxy Configuration Error . . . . . . . . . . . . . . 18
2.3.32. Proxy Loop Detected . . . . . . . . . . . . . . . . . 18
2.4. Defining New Proxy Error Types . . . . . . . . . . . . . 18
3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 19
4. Security Considerations . . . . . . . . . . . . . . . . . . . 19
5. References . . . . . . . . . . . . . . . . . . . . . . . . . 20
5.1. Normative References . . . . . . . . . . . . . . . . . . 20
5.2. Informative References . . . . . . . . . . . . . . . . . 20
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 21
1. Introduction
HTTP intermediaries -- including both forward proxies and gateways
(also known as "reverse proxies") -- have become an increasingly
significant part of HTTP deployments. In particular, reverse proxies
and Content Delivery Networks (CDNs) form part of the critical
infrastructure of many Web sites.
Typically, HTTP intermediaries forward requests towards the origin
server and then forward their responses back to clients. However, if
an error occurs before a response is obtained from upstream, the
response is often generated by the intermediary itself.
HTTP accommodates these types of errors with a few status codes; for
example, 502 Bad Gateway and 504 Gateway Timeout. However,
experience has shown that more information is necessary to aid
debugging and communicate what's happened to the client.
Additionally, intermediaries sometimes want to convey additional
information about their handling of a response, even if they did not
generate it.
To enable these uses, Section 2 defines a new HTTP response field to
allow intermediaries to convey details of their handling of a
response. Section 2.1 enumerates the information that can be added
to the field by intermediaries, which can be extended as per
Section 2.2. Section 2.3 defines a set of error types for use when a
proxy encounters an issue when obtaining a response for the request;
these can likewise be extended as per Section 2.4.
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1.1. Notational Conventions
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.
This specification uses Structured Fields [RFC8941] to specify syntax
and parsing, and ABNF [RFC5234] as a shorthand for that syntax. The
terms sf-list, sf-item, sf-string, sf-token, sf-integer and key refer
to the structured types defined therein.
Note that in this specification, "proxy" is used to indicate both
forward and reverse proxies, otherwise known as gateways. "Next hop"
indicates the connection in the direction leading to the origin
server for the request.
2. The Proxy-Status HTTP Field
The Proxy-Status HTTP response field allows an intermediary to convey
additional information about its handling of a response and its
associated request.
It is a List ([RFC8941], Section 3.1):
Proxy-Status = sf-list
Each member of the list represents an intermediary that has handled
the response. The first member of the list represents the
intermediary closest to the origin server, and the last member of the
list represents the intermediary closest to the user agent.
For example:
Proxy-Status: FooProxy, ExampleCDN
indicates that this response was handled first by FooProxy and then
ExampleCDN.
Intermediaries determine when it is appropriate to add the Proxy-
Status field to a response. Some might decide to append to it to all
responses, whereas others might only do so when specifically
configured to, or when the request contains a header that activates a
debugging mode.
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Each member of the list identifies the intermediary that inserted the
value, and MUST have a type of either sf-string or sf-token.
Depending on the deployment, this might be a product or service name
(e.g., ExampleProxy or "Example CDN"), a hostname ("proxy-
3.example.com"), an IP address, or a generated string.
Parameters on each member convey additional information about that
intermediary's handling of the response and its associated request;
see Section 2.1. While all of these parameters are OPTIONAL,
intermediaries are encouraged to provide as much information as
possible (but see Section 4 for security considerations in doing so).
When adding a value to the Proxy-Status field, intermediaries SHOULD
preserve the existing members of the field, to allow debugging of the
entire chain of intermediaries handling the request.
Proxy-Status MAY be sent in HTTP trailers. For example, if an
intermediary is streaming a response and the upstream connection
suddenly terminates, Proxy-Status can only be appended to the
trailers of the outgoing message, since the headers have already been
sent. As with all trailers, it might be silently discarded along the
path to the user agent, so this SHOULD NOT be done unless it is not
possible to send it in headers, and an intermediary MUST NOT send
Proxy-Status as a trailer field unless it has also sent a
corresponding Proxy-Status header field in the same message, so that
the trailer value's ordering relative to other intermediaries is
preserved.
Origin servers MUST NOT generate the Proxy-Status field.
2.1. Proxy-Status Parameters
This section lists parameters that can be used on the members of the
Proxy-Status field. Unrecognised parameters MUST be ignored.
2.1.1. error
The "error" parameter's value is an sf-token that is a Proxy Error
Type. When present, it indicates that the proxy encountered an issue
when obtaining a response.
Unless a Proxy Error Type specifies otherwise, the presences of error
often, but not always, indicates that response was generated by the
proxy, not the origin server or any other upstream server. For
example, a proxy might attempt to correct an error, or part of a
response might be forwarded before the error is encountered.
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Section 2.3 lists the Proxy Error Types defined in this document; new
ones can be defined using the procedure outlined in Section 2.4.
For example:
HTTP/1.1 504 Gateway Timeout
Proxy-Status: SomeCDN; error=connection_timeout
indicates that this 504 response was generated by SomeCDN, due to a
connection timeout when going forward.
Or:
HTTP/1.1 429 Too Many Requests
Proxy-Status: SomeReverseProxy; error=http_request_error
indicates that this 429 Too Many Requests response was generated by
the intermediary, not the origin.
When sending the error parameter, the most specific Proxy Error Type
SHOULD be sent, provided that it accurately represents the error
condition. If an appropriate Proxy Error Type is not defined, there
are a number of generic error types (e.g., proxy_internal_error,
http_protocol_error) that can be used. If they are not suitable,
consider registering a new Proxy Error Type (see Section 2.4).
Each Proxy Error Type has a Recommended HTTP Status Code. When
generating a HTTP response containing "error", its HTTP status code
SHOULD be set to the Recommended HTTP Status Code. However, there
may be circumstances (e.g., for backwards compatibility with previous
behaviours, a status code has already been sent) when another status
code might be used.
Proxy Error Types can also define any number of extra parameters for
use with that type. Their use, like all parameters, is optional. As
a result, if an extra parameter is used with a Proxy Error Type for
which it is not defined, it will be ignored.
2.1.2. next-hop
The "next-hop" parameter's value is an sf-string or sf-token that
identifies the intermediary or origin server selected (and used, if
contacted) for this response. It might be a hostname, IP address, or
alias.
For example:
Proxy-Status: cdn.example.org; next-hop=backend.example.org
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2.1.3. next-protocol
The "next-protocol" parameter's value indicates the ALPN protocol
identifier [RFC7301] used by the intermediary to connect to the next
hop. This is only applicable when that connection was actually
established.
The value MUST be either an sf-token or sf-binary. If the protocol
identifier is able to be expressed as an sf-token using UTF-8
encoding, that form MUST be used.
For example:
Proxy-Status: "proxy.example.org"; next-protocol=h2
2.1.4. received-status
The "received-status" parameter's value indicates the HTTP status
code that the intermediary received from the next hop server.
The value MUST be an sf-integer.
For example:
Proxy-Status: ExampleProxy; received-status=200
2.1.5. details
The "details" parameter's value is an sf-string containing additional
information not captured anywhere else. This can include
implementation-specific or deployment-specific information.
For example:
Proxy-Status: ExampleProxy; error="http_protocol_error";
details="Malformed response header - space before colon"
2.2. Defining New Proxy-Status Parameters
New Proxy-Status Parameters can be defined by registering them in the
HTTP Proxy-Status Parameters registry.
Registration requests are reviewed and approved by a Designated
Expert, as per [RFC8126], Section 4.5. A specification document is
appreciated, but not required.
The Expert(s) should consider the following factors when evaluating
requests:
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* Community feedback
* If the value is sufficiently well-defined
* Generic parameters are preferred over vendor-specific,
application-specific or deployment-specific values. If a generic
value cannot be agreed upon in the community, the parameter's name
should be correspondingly specific (e.g., with a prefix that
identifies the vendor, application or deployment).
* Parameter names should not conflict with registered extra
parameters in the Proxy Error Type Registry.
Registration requests should use the following template:
* Name: [a name for the Proxy-Status Parameter that matches key]
* Description: [a description of the parameter semantics and value]
* Reference: [to a specification defining this parameter]
See the registry at https://iana.org/assignments/http-proxy-status
(https://iana.org/assignments/http-proxy-status) for details on where
to send registration requests.
2.3. Proxy Error Types
This section lists the Proxy Error Types defined by this document.
See Section 2.4 for information about defining new Proxy Error Types.
2.3.1. DNS Timeout
* Name: dns_timeout
* Description: The intermediary encountered a timeout when trying to
find an IP address for the next hop hostname.
* Extra Parameters: None.
* Recommended HTTP status code: 504
2.3.2. DNS Error
* Name: dns_error
* Description: The intermediary encountered a DNS error when trying
to find an IP address for the next hop hostname.
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* Extra Parameters:
- rcode: A sf-string conveying the DNS RCODE that indicates the
error type. See [RFC8499], Section 3.
- info-code: A sf-integer conveying the Extended DNS Error Code
info-code. See [RFC8914].
* Recommended HTTP status code: 502
2.3.3. Destination Not Found
* Name: destination_not_found
* Description: The intermediary cannot determine the appropriate
next hop to use for this request; for example, it may not be
configured. Note that this error is specific to gateways, which
typically require specific configuration to identify the "backend"
server; forward proxies use in-band information to identify the
origin server.
* Extra Parameters: None.
* Recommended HTTP status code: 500
2.3.4. Destination Unavailable
* Name: destination_unavailable
* Description: The intermediary considers the next hop to be
unavailable; e.g., recent attempts to communicate with it may have
failed, or a health check may indicate that it is down.
* Extra Parameters: None.
* Recommended HTTP status code: 503
2.3.5. Destination IP Prohibited
* Name: destination_ip_prohibited
* Description: The intermediary is configured to prohibit
connections to the next hop IP address.
* Extra Parameters: None.
* Recommended HTTP status code: 502
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2.3.6. Destination IP Unroutable
* Name: destination_ip_unroutable
* Description: The intermediary cannot find a route to the next hop
IP address.
* Extra Parameters: None.
* Recommended HTTP status code: 502
2.3.7. Connection Refused
* Name: connection_refused
* Description: The intermediary's connection to the next hop was
refused.
* Extra Parameters: None.
* Recommended HTTP status code: 502
2.3.8. Connection Terminated
* Name: connection_terminated
* Description: The intermediary's connection to the next hop was
closed before complete response was received.
* Extra Parameters: None.
* Recommended HTTP status code: 502
* Notes: Responses with this error type might not have been
generated by the intermediary.
2.3.9. Connection Timeout
* Name: connection_timeout
* Description: The intermediary's attempt to open a connection to
the next hop timed out.
* Extra Parameters: None.
* Recommended HTTP status code: 504
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2.3.10. Connection Read Timeout
* Name: connection_read_timeout
* Description: The intermediary was expecting data on a connection
(e.g., part of a response), but did not receive any new data in a
configured time limit.
* Extra Parameters: None.
* Recommended HTTP status code: 504
* Notes: Responses with this error type might not have been
generated by the intermediary.
2.3.11. Connection Write Timeout
* Name: connection_write_timeout
* Description: The intermediary was attempting to write data to a
connection, but was not able to (e.g., because its buffers were
full).
* Extra Parameters: None.
* Recommended HTTP status code: 504
* Notes: Responses with this error type might not have been
generated by the intermediary.
2.3.12. Connection Limit Reached
* Name: connection_limit_reached
* Description: The intermediary is configured to limit the number of
connections it has to the next hop, and that limit has been
passed.
* Extra Parameters: None.
* Recommended HTTP status code: 503
2.3.13. TLS Protocol Error
* Name: tls_protocol_error
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* Description: The intermediary encountered a TLS error when
communicating with the next hop, either during handshake or
afterwards.
* Extra Parameters: None.
* Recommended HTTP status code: 502
* Notes: Responses with this error type might not have been
generated by the intermediary.
Note that additional information about the error can be recorded in
the details parameter (as is the case for all errors).
2.3.14. TLS Certificate Error
* Name: tls_certificate_error
* Description: The intermediary encountered an error when verifying
the certificate presented by the next hop.
* Extra Parameters: None.
* Recommended HTTP status code: 502
Note that additional information about the error can be recorded in
the details parameter (as is the case for all errors).
2.3.15. TLS Alert Received
* Name: tls_alert_received
* Description: The intermediary received a TLS alert from the next
hop.
* Extra Parameters:
- alert-message: an sf-token containing the applicable
description string from the TLS Alerts registry.
* Recommended HTTP status code: 502
* Notes: Responses with this error type might not have been
generated by the intermediary.
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2.3.16. HTTP Request Error
* Name: http_request_error
* Description: The intermediary is generating a client (4xx)
response on the origin's behalf. Applicable status codes include
(but are not limited to) 400, 403, 405, 406, 408, 411, 413, 414,
415, 416, 417, 429.
* Extra Parameters:
- status-code: an sf-integer containing the generated status
code.
- status-phrase: an sf-string containing the generated status
phrase.
* Recommended HTTP status code: The applicable 4xx status code
* Notes: This type helps distinguish between responses generated by
intermediaries from those generated by the origin.
2.3.17. HTTP Request Denied
* Name: http_request_denied
* Description: The intermediary rejected the HTTP request based on
its configuration and/or policy settings. The request wasn't
forwarded to the next hop.
* Extra Parameters: None.
* Recommended HTTP status code: 403
2.3.18. HTTP Incomplete Response
* Name: http_response_incomplete
* Description: The intermediary received an incomplete response to
the request from the next hop.
* Extra Parameters: None.
* Recommended HTTP status code: 502
* Notes: Responses with this error type might not have been
generated by the intermediary.
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2.3.19. HTTP Response Header Section Too Large
* Name: http_response_header_section_size
* Description: The intermediary received a response to the request
whose header section was considered too large.
* Extra Parameters:
- header-section-size: an sf-integer indicating how large the
headers received were. Note that they might not be complete;
i.e., the intermediary may have discarded or refused additional
data.
* Recommended HTTP status code: 502
* Notes: Responses with this error type might not have been
generated by the intermediary.
2.3.20. HTTP Response Header Too Large
* Name: http_response_header_size
* Description: The intermediary received a response to the request
containing an individual header line that was considered too
large.
* Extra Parameters:
- header-name: an sf-string indicating the name of the header
that triggered the error.
- header-size: an sf-integer indicating the size of the header
that triggered the error.
* Recommended HTTP status code: 502
* Notes: Responses with this error type might not have been
generated by the intermediary.
2.3.21. HTTP Response Body Too Large
* Name: http_response_body_size
* Description: The intermediary received a response to the request
whose body was considered too large.
* Extra Parameters:
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- body-size: an sf-integer indicating how large the body received
was. Note that it may not have been complete; i.e., the
intermediary may have discarded or refused additional data.
* Recommended HTTP status code: 502
* Notes: Responses with this error type might not have been
generated by the intermediary.
2.3.22. HTTP Response Trailer Section Too Large
* Name: http_response_trailer_section_size
* Description: The intermediary received a response to the request
whose trailer section was considered too large.
* Extra Parameters:
- trailer-section-size: an sf-integer indicating how large the
trailers received were. Note that they might not be complete;
i.e., the intermediary may have discarded or refused additional
data.
* Recommended HTTP status code: 502
* Notes: Responses with this error type might not have been
generated by the intermediary.
2.3.23. HTTP Response Trailer Too Large
* Name: http_response_trailer_size
* Description: The intermediary received a response to the request
containing an individual trailer line that was considered too
large.
* Extra Parameters:
- trailer-name: an sf-string indicating the name of the trailer
that triggered the error.
- trailer-size: an sf-integer indicating the size of the trailer
that triggered the error.
* Recommended HTTP status code: 502
* Notes: Responses with this error type might not have been
generated by the intermediary.
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2.3.24. HTTP Response Transfer-Coding Error
* Name: http_response_transfer_coding
* Description: The intermediary encountered an error decoding the
transfer-coding of the response.
* Extra Parameters:
- coding: an sf-token containing the specific coding that caused
the error.
* Recommended HTTP status code: 502
* Notes: Responses with this error type might not have been
generated by the intermediary.
2.3.25. HTTP Response Content-Coding Error
* Name: http_response_content_coding
* Description: The intermediary encountered an error decoding the
content-coding of the response.
* Extra Parameters:
- coding: an sf-token containing the specific coding that caused
the error.
* Recommended HTTP status code: 502
* Notes: Responses with this error type might not have been
generated by the intermediary.
2.3.26. HTTP Response Timeout
* Name: http_response_timeout
* Description: The intermediary reached a configured time limit
waiting for the complete response.
* Extra Parameters: None.
* Recommended HTTP status code: 504
* Notes: Responses with this error type might not have been
generated by the intermediary.
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2.3.27. HTTP Upgrade Failed
* Name: http_upgrade_failed
* Description: The HTTP Upgrade between the intermediary and the
next hop failed.
* Extra Parameters: None.
* Recommended HTTP status code: 502
2.3.28. HTTP Protocol Error
* Name: http_protocol_error
* Description: The intermediary encountered a HTTP protocol error
when communicating with the next hop. This error should only be
used when a more specific one is not defined.
* Extra Parameters: None.
* Recommended HTTP status code: 502
* Notes: Responses with this error type might not have been
generated by the intermediary.
Note that additional information about the error can be recorded in
the details parameter (as is the case for all errors).
2.3.29. Proxy Internal Response
* Name: proxy_internal_response
* Description: The intermediary generated the response locally,
without attempting to connect to the next hop (e.g. in response to
a request to a debug endpoint terminated at the intermediary).
* Extra Parameters: None.
* Recommended HTTP status code:
2.3.30. Proxy Internal Error
* Name: proxy_internal_error
* Description: The intermediary encountered an internal error
unrelated to the origin.
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* Extra Parameters: None
* Recommended HTTP status code: 500
Note that additional information about the error can be recorded in
the details parameter (as is the case for all errors).
2.3.31. Proxy Configuration Error
* Name: proxy_configuration_error
* Description: The intermediary encountered an error regarding its
configuration.
* Extra Parameters: None
* Recommended HTTP status code: 500
Note that additional information about the error can be recorded in
the details parameter (as is the case for all errors).
2.3.32. Proxy Loop Detected
* Name: proxy_loop_detected
* Description: The intermediary tried to forward the request to
itself, or a loop has been detected using different means (e.g.
[RFC8586]).
* Extra Parameters: None.
* Recommended HTTP status code: 502
2.4. Defining New Proxy Error Types
New Proxy Error Types can be defined by registering them in the HTTP
Proxy Error Types registry.
Registration requests are reviewed and approved by a Designated
Expert, as per [RFC8126], Section 4.5. A specification document is
appreciated, but not required.
The Expert(s) should consider the following factors when evaluating
requests:
* Community feedback
* If the value is sufficiently well-defined
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* Generic types are preferred over vendor-specific, application-
specific or deployment-specific values. If a generic value cannot
be agreed upon in the community, the types's name should be
correspondingly specific (e.g., with a prefix that identifies the
vendor, application or deployment).
* Extra Parameters should not conflict with registered Proxy-Status
parameters.
Registration requests should use the following template:
* Name: [a name for the Proxy Error Type that matches sf-token]
* Description: [a description of the conditions that generate the
Proxy Error Type]
* Extra Parameters: [zero or more optional parameters, along with
their allowable type(s)]
* Recommended HTTP status code: [the appropriate HTTP status code
for this entry]
* Notes: [optional]
If the Proxy Error Type might occur in responses that are not
generated by the intermediary -- for example, when the error is
detected during response content processing and a Proxy-Status
trailer field is appended -- that SHOULD be explained in the Notes.
See the registry at https://iana.org/assignments/http-proxy-status
(https://iana.org/assignments/http-proxy-status) for details on where
to send registration requests.
3. IANA Considerations
Upon publication, please create the HTTP Proxy-Status Parameters
registry and the HTTP Proxy Error Types registry at
https://iana.org/assignments/http-proxy-statuses
(https://iana.org/assignments/http-proxy-statuses) and populate them
with the types defined in Section 2.1 and Section 2.3 respectively;
see Section 2.2 and Section 2.4 for its associated procedures.
4. Security Considerations
One of the primary security concerns when using Proxy-Status is
leaking information that might aid an attacker. For example,
information about the intermediary's configuration and back-end
topology can be exposed.
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As a result, care needs to be taken when deciding to generate a
Proxy-Status field. Note that intermediaries are not required to
generate a Proxy-Status field in any response, and can conditionally
generate them based upon request attributes (e.g., authentication
tokens, IP address).
Likewise, generation of all parameters is optional.
5. References
5.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/rfc/rfc2119>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/rfc/rfc8126>.
[RFC8499] Hoffman, P., Sullivan, A., and K. Fujiwara, "DNS
Terminology", BCP 219, RFC 8499, DOI 10.17487/RFC8499,
January 2019, <https://www.rfc-editor.org/rfc/rfc8499>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/rfc/rfc8174>.
[RFC8941] Nottingham, M. and P-H. Kamp, "Structured Field Values for
HTTP", RFC 8941, DOI 10.17487/RFC8941, February 2021,
<https://www.rfc-editor.org/rfc/rfc8941>.
[RFC7301] Friedl, S., Popov, A., Langley, A., and E. Stephan,
"Transport Layer Security (TLS) Application-Layer Protocol
Negotiation Extension", RFC 7301, DOI 10.17487/RFC7301,
July 2014, <https://www.rfc-editor.org/rfc/rfc7301>.
[RFC8914] Kumari, W., Hunt, E., Arends, R., Hardaker, W., and D.
Lawrence, "Extended DNS Errors", RFC 8914,
DOI 10.17487/RFC8914, October 2020,
<https://www.rfc-editor.org/rfc/rfc8914>.
5.2. Informative References
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[RFC5234] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008,
<https://www.rfc-editor.org/rfc/rfc5234>.
[RFC8586] Ludin, S., Nottingham, M., and N. Sullivan, "Loop
Detection in Content Delivery Networks (CDNs)", RFC 8586,
DOI 10.17487/RFC8586, April 2019,
<https://www.rfc-editor.org/rfc/rfc8586>.
Authors' Addresses
Mark Nottingham
Fastly
Prahran VIC
Australia
Email: mnot@mnot.net
URI: https://www.mnot.net/
Piotr Sikora
Google
Email: piotrsikora@google.com
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