Network Working Group E. Hammer-Lahav, Ed.
Internet-Draft Yahoo!
Intended status: Standards Track July 6, 2009
Expires: January 7, 2010
The OAuth Protocol: Authentication
draft-ietf-oauth-authentication-00
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Abstract
This document specifies the OAuth protocol authentication method.
OAuth allows clients to access server resources on behalf of another
party (such a different client or an end user). This document
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defines an HTTP authentication method which supports the ability to
include two sets of credential with each request, one identifying the
client and another identifying the resource owner on whose behalf the
request is made.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Notational Conventions . . . . . . . . . . . . . . . . . . . . 4
3. Authenticated Requests . . . . . . . . . . . . . . . . . . . . 4
3.1. Protocol Parameters . . . . . . . . . . . . . . . . . . . 5
3.2. Nonce and Timestamp . . . . . . . . . . . . . . . . . . . 6
3.3. Signature . . . . . . . . . . . . . . . . . . . . . . . . 6
3.3.1. Signature Base String . . . . . . . . . . . . . . . . 7
3.3.2. HMAC-SHA1 . . . . . . . . . . . . . . . . . . . . . . 11
3.3.3. RSA-SHA1 . . . . . . . . . . . . . . . . . . . . . . . 12
3.3.4. PLAINTEXT . . . . . . . . . . . . . . . . . . . . . . 13
3.4. Parameter Transmission . . . . . . . . . . . . . . . . . . 13
3.4.1. Authorization Header . . . . . . . . . . . . . . . . . 13
3.4.2. Form-Encoded Body . . . . . . . . . . . . . . . . . . 14
3.4.3. Request URI Query . . . . . . . . . . . . . . . . . . 15
3.5. Server Response . . . . . . . . . . . . . . . . . . . . . 15
3.6. Percent Encoding . . . . . . . . . . . . . . . . . . . . . 16
4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 17
5. Security Considerations . . . . . . . . . . . . . . . . . . . 17
5.1. RSA-SHA1 Signature Method . . . . . . . . . . . . . . . . 17
5.2. PLAINTEXT Signature Method . . . . . . . . . . . . . . . . 17
5.3. Confidentiality of Requests . . . . . . . . . . . . . . . 17
5.4. Spoofing by Counterfeit Servers . . . . . . . . . . . . . 17
5.5. Proxying and Caching of Authenticated Content . . . . . . 18
5.6. Plaintext Storage of Credentials . . . . . . . . . . . . . 18
5.7. Secrecy of the Client Credentials . . . . . . . . . . . . 18
5.8. Cryptographic Attacks . . . . . . . . . . . . . . . . . . 18
5.9. Signature Base String Limitations . . . . . . . . . . . . 19
Appendix A. Examples . . . . . . . . . . . . . . . . . . . . . . 19
Appendix B. Acknowledgments . . . . . . . . . . . . . . . . . . . 19
Appendix C. Document History . . . . . . . . . . . . . . . . . . 19
6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 20
6.1. Normative References . . . . . . . . . . . . . . . . . . . 20
6.2. Informative References . . . . . . . . . . . . . . . . . . 21
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 21
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1. Introduction
The OAuth protocol provides a method for servers to allow third-party
access to protected resources, without forcing their end users to
share their credentials. This pattern is common among services that
allow third-party developers to extend the service functionality, by
building applications using an open API.
For example, a web user (resource owner) can grant a printing service
(client) access to its private photos stored at a photo sharing
service (server), without sharing its credentials with the printing
service. Instead, the user authenticates directly with the photo
sharing service and issue the printing service delegation-specific
credentials.
OAuth introduces a third role to the traditional client-server
authentication model: the resource owner. In the OAuth model, the
client requests access to resources hosted by the server but not
controlled by the client, but by the resource owner. In addition,
OAuth allows the server to verify not only the resource owner's
credentials, but also those of the client making the request.
In order for the client to access resources, it first has to obtain
permission from the resource owner. This permission is expressed in
the form of a token and matching shared-secret. The purpose of the
token is to substitute the need for the resource owner to share its
server credentials (usually a username and password pair) with the
client. Unlike server credentials, tokens can be issued with a
restricted scope and limited lifetime.
This specification consists of two parts. This document defines a
method for making authenticated HTTP requests using two sets of
credentials, one identifying the client making the request, and a
second identifying the resource owner on whose behalf the request is
being made.
[draft-ietf-oauth-web-delegation] defines a redirection-based user
agent process for end users to authorize client access to their
resources, by authenticating directly with the server and
provisioning tokens to the client for use with the authentication
method.
1.1. Terminology
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client
An HTTP client (per [RFC2616]) capable of making OAuth-
authenticated requests (Section 3).
server
An HTTP server (per [RFC2616]) capable of accepting OAuth-
authenticated requests (Section 3).
protected resource
An access-restricted resource (per [RFC2616]) which can be
obtained from the server using an OAuth-authenticated request
(Section 3).
resource owner
An entity capable of accessing and controlling protected
resources by using credentials to authenticate with the server.
token
An unique identifier issued by the server and used by the
client to associate authenticated requests with the resource
owner whose authorization is requested or has been obtained by
the client. Tokens have a matching shared-secret that is used
by the client to establish its ownership of the token, and its
authority to represent the resource owner.
2. Notational Conventions
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in [RFC2119].
3. Authenticated Requests
The HTTP authentication methods defined by [RFC2617], enable clients
to make authenticated HTTP requests. Clients using these methods
gain access to protected resource by using their server credentials
(typically a username and password pair), which allows the server to
verify their authenticity. Using these methods for delegation
requires the client to pretend it was the resource owner.
OAuth provides a method designed to include two sets of credentials
with each request, one to identify the client, and another to
identify the resource owner. Before a client can make authenticated
requests on behalf of the resource owner, it must obtain a token
authorized by the resource owner. [draft-ietf-oauth-web-delegation]
provides one such method in which the client can obtain a token
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authorized by the resource owner.
The client credentials take the form of a unique identifier, and an
associated share-secret or RSA key pair. Prior to making
authenticated requests, the client establishes a set of credentials
with the server. The process and requirements for provisioning these
are outside the scope of this specification. Implementers are urged
to consider the security ramification of using client credentials,
some of which are described in Section 5.7.
Making authenticated requests requires prior knowledge of the
server's configuration. OAuth provides multiple methods for
including protocol parameters in requests (Section 3.4), as well as
multiple methods for the client to prove its rightful ownership of
the credentials used (Section 3.3). The way in which clients
discovery the required configuration is outside the scope of this
specification.
3.1. Protocol Parameters
An OAuth-authenticated request includes several protocol parameters.
Each parameter name begins with the "oauth_" prefix, and the
parameter names and values are case sensitive. Protocol parameters
MUST NOT appear more than once per request. The parameters are:
oauth_consumer_key
The identifier portion of the client credentials (equivalent to
a username). The parameter name reflects a deprecated term
(Consumer Key) used in previous revisions of the specification,
and has been retained to maintain backward compatibility.
oauth_token
The token value used to associate the request with the resource
owner. If the request is not associated with a resource owner
(no token), clients MAY omit the parameter.
oauth_signature_method
The name of the signature method used by the client to sign the
request, as defined in Section 3.3.
oauth_signature
The signature value as defined in Section 3.3.
oauth_timestamp
The timestamp value as defined in Section 3.2.
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oauth_nonce
The nonce value as defined in Section 3.2.
oauth_version
The protocol version. If omitted, the protocol version
defaults to "1.0".
Server-specific request parameters MUST NOT begin with the "oauth_"
prefix.
3.2. Nonce and Timestamp
Unless otherwise specified by the server, the timestamp is expressed
in the number of seconds since January 1, 1970 00:00:00 GMT. The
timestamp value MUST be a positive integer and MUST be equal or
greater than the timestamp used in previous requests with the same
client credentials and token credentials combination.
A nonce is a random string, uniquely generated to allows the server
to verify that a request has never been made before and helps prevent
replay attacks when requests are made over a non-secure channel. The
nonce value MUST be unique across all requests with the same
timestamp, client credentials, and token combinations.
To avoid the need to retain an infinite number of nonce values for
future checks, servers MAY choose to restrict the time period after
which a request with an old timestamp is rejected. Server applying
such restriction SHOULD provide a way for the client to sync its
clock with the server's clock.
3.3. Signature
OAuth-authenticated requests can have two sets of credentials
included via the "oauth_consumer_key" parameter and the "oauth_token"
parameter. In order for the server to verify the authenticity of the
request and prevent unauthorized access, the client needs to prove it
is the rightful owner of the credentials. This is accomplished using
the shared-secret (or RSA key) part of each set of credentials.
OAuth provides three methods for the client to prove its rightful
ownership of the credentials: "HMAC-SHA1", "RSA-SHA1", and
"PLAINTEXT". These methods are generally referred to as signature
methods, even though "PLAINTEXT" does not involve a signature. In
addition, "RSA-SHA1" utilizes an RSA key instead of the shared-
secrets associated with the client credentials.
OAuth does not mandate a particular signature method, as each
implementation can have its own unique requirements. Servers are
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free to implement and document their own custom methods.
Recommending any particular method is beyond the scope of this
specification.
The client declares which signature method is used via the
"oauth_signature_method" parameter. It then generates a signature
(or a sting of an equivalent value), and includes it in the
"oauth_signature" parameter. The server verifies the signature as
specified for each method.
The signature process does not change the request or its parameter,
with the exception of the "oauth_signature" parameter.
3.3.1. Signature Base String
The signature base string is a consistent, reproducible concatenation
of several request elements into a single string. The string is used
as an input to the "HMAC-SHA1" and "RSA-SHA1" signature methods, or
potential future extension.
The signature base string does not cover the entire HTTP request.
Most notably, it does not include the entity-body in most requests,
nor does it include most HTTP entity-headers. The importance of the
signature base string scope is that the authenticity of the excluded
components cannot be verified using the signature.
3.3.1.1. Collect Request Parameters
The signature base string includes a specific set of request
parameters. In order for the parameter to be included in the
signature base string, they MUST be used in their unencoded form.
For example, the URI:
http://example.com/request?b5=%3D%253D&a3=a&c%40=&a2=r%20b&c2&a3=2q
contains the following raw-form parameters:
+------+-------+
| Name | Value |
+------+-------+
| b5 | =%3D |
| a3 | a |
| c@ | |
| a2 | r b |
| c2 | |
| a3 | 2q |
+------+-------+
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Note that the value of "b5" is "=%3D" and not "==". Both "c@" and
"c2" have empty values.
The request parameters, which include both protocol parameters and
request-specific parameters, are extracted and restored to their
original unencoded form, from the following sources:
o The OAuth HTTP Authorization header (Section 3.4.1). The "realm"
parameter MUST be excluded if present.
o The HTTP request entity-body, but only if:
* The entity-body is single-part.
* The entity-body follows the encoding requirements of the
"application/x-www-form-urlencoded" content-type as defined by
[W3C.REC-html40-19980424].
* The HTTP request entity-header includes the "Content-Type"
header set to "application/x-www-form-urlencoded".
o The query component of the HTTP request URI as defined by
[RFC3986] section 3.
The "oauth_signature" parameter MUST be excluded if present.
In many cases, clients have direct access to the parameters in their
original, unencoded form. In such cases, clients SHOULD use the
unencoded values instead of extracting them. This option is not
available for servers when validating incoming requests. Even though
the parameters are encoded again in the process, they are decoded
because each of the three sources uses a different encoding
algorithm.
The output of this step is a list of unencoded parameter name / value
pairs.
3.3.1.2. Normalize Request Parameters
The parameter collected in Section 3.3.1.1 are normalized into a
single string as follows:
1. First, the name and value of each parameter are encoded
(Section 3.6).
2. The parameters are sorted by name, using lexicographical byte
value ordering. If two or more parameters share the same name,
they are sorted by their value.
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3. The name of each parameter is concatenated to its corresponding
value using an "=" character (ASCII code 61) as separator, even
if the value is empty.
4. The sorted name / value pairs are concatenated together into a
single string by using an "&" character (ASCII code 38) as
separator.
For example, the list of parameters from the previous section would
be normalized as follows:
Encoded:
+------+----------+
| Name | Value |
+------+----------+
| b5 | %3D%253D |
| a3 | a |
| c%40 | |
| a2 | r%20b |
| c2 | |
| a3 | 2q |
+------+----------+
Sorted:
+------+----------+
| Name | Value |
+------+----------+
| a2 | r%20b |
| a3 | 2q |
| a3 | a |
| b5 | %3D%253D |
| c%40 | |
| c2 | |
+------+----------+
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Concatenated Pairs:
+-------------+
| Name=Value |
+-------------+
| a2=r%20b |
| a3=2q |
| a3=a |
| b5=%3D%253D |
| c%40= |
| c2= |
+-------------+
And concatenated together into a single string:
a2=r%20b&a3=2q&a3=a&b5=%3D%253D&c%40=&c2=
3.3.1.3. Construct Base String URI
The signature base string incorporates the scheme, authority, and
path of the request URI as defined by [RFC3986] section 3. The
request URI query component is included through the normalized
parameters string (Section 3.3.1.2), and the fragment component is
excluded.
This is done by constructing a base string URI representing the
request without the query or fragment components. The base string
URI is constructed as follows:
1. The scheme and host MUST be in lowercase.
2. The host and port values MUST match the content of the HTTP
request "Host" header, if present. If the "Host" header is not
present, the client MUST use the hostname and port used to make
the request. Servers SHOULD remove potential ambiguity in such
cases by specifying the expected host value.
3. The port MUST be included if it is not the default port for the
scheme, and MUST be excluded if it is the default. Specifically,
the port MUST be excluded when an "http" request uses port 80 or
when an "https" request uses port 443. All other non-default
port numbers MUST be included.
4. If the URI includes an empty path, it MUST be included as "/".
For example:
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+----------------------------------+-------------------------------+
| The request URI | Is included in base string as |
+----------------------------------+-------------------------------+
| HTTP://EXAMPLE.com:80/r/x?id=123 | http://example.com/r/x |
| https://example.net:8080?q=1#top | https://example.net:8080/ |
+----------------------------------+-------------------------------+
3.3.1.4. Concatenate Base String Elements
Finally, the signature base string is put together by concatenating
its elements together. The elements MUST be concatenated in the
following order:
1. The HTTP request method in uppercase. For example: "HEAD",
"GET", "POST", etc. If the request uses a custom HTTP method, it
MUST be encoded (Section 3.6).
2. An "&" character (ASCII code 38).
3. The base string URI from Section 3.3.1.3, after being encoded
(Section 3.6).
4. An "&" character (ASCII code 38).
5. The normalized request parameters string from Section 3.3.1.2,
after being encoded (Section 3.6).
3.3.2. HMAC-SHA1
The "HMAC-SHA1" signature method uses the HMAC-SHA1 signature
algorithm as defined in [RFC2104]:
digest = HMAC-SHA1 (key, text)
The HMAC-SHA1 function variables are used in following way:
text
is set to the value of the signature base string from
Section 3.3.1.4.
key
is set to the concatenated values of:
1. The client shared-secret, after being encoded
(Section 3.6).
2. An "&" character (ASCII code 38), which MUST be included
even when either secret is empty.
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3. The token shared-secret, after being encoded
(Section 3.6).
digest
is used to set the value of the "oauth_signature" protocol
parameter, after the result octet string is base64-encoded per
[RFC2045] section 6.8.
3.3.3. RSA-SHA1
The "RSA-SHA1" signature method uses the RSASSA-PKCS1-v1_5 signature
algorithm as defined in [RFC3447] section 8.2 (also known as PKCS#1),
using SHA-1 as the hash function for EMSA-PKCS1-v1_5. To use this
method, the client MUST have established client credentials with the
server which included its RSA public key (in a manner which is beyond
the scope of this specification).
The signature base string is signed using the client's RSA private
key per [RFC3447] section 8.2.1:
S = RSASSA-PKCS1-V1_5-SIGN (K, M)
Where:
K
is set to the client's RSA private key,
M
is set to the value of the signature base string from
Section 3.3.1.4, and
S
is the result signature used to set the value of the
"oauth_signature" protocol parameter, after the result octet
string is base64-encoded per [RFC2045] section 6.8.
The server verifies the signature per [RFC3447] section 8.2.2:
RSASSA-PKCS1-V1_5-VERIFY ((n, e), M, S)
Where:
(n, e)
is set to the client's RSA public key,
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M
is set to the value of the signature base string from
Section 3.3.1.4, and
S
is set to the octet string value of the "oauth_signature"
protocol parameter received from the client.
3.3.4. PLAINTEXT
The "PLAINTEXT" method does not employ a signature algorithm and does
not provide any security as it transmits secrets in the clear. It
SHOULD only be used with a transport-layer mechanisms such as TLS or
SSL. It does not use the signature base string.
The "oauth_signature" protocol parameter is set to the concatenated
value of:
1. The client shared-secret, after being encoded (Section 3.6).
2. An "&" character (ASCII code 38), which MUST be included even
when either secret is empty.
3. The token shared-secret, after being encoded (Section 3.6).
3.4. Parameter Transmission
When making an OAuth-authenticated request, protocol parameters SHALL
be included in the request using one and only one of the following
locations, listed in order of decreasing preference:
1. The HTTP "Authorization" header as described in Section 3.4.1.
2. The HTTP request entity-body as described in Section 3.4.2.
3. The HTTP request URI query as described in Section 3.4.3.
In addition to these three methods, future extensions may provide
other methods for including protocol parameters in the request.
3.4.1. Authorization Header
Protocol parameters can be transmitted using the HTTP "Authorization"
header as defined by [RFC2617] with the auth-scheme name set to
"OAuth" (case-insensitive).
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For example:
Authorization: OAuth realm="http://server.example.com/",
oauth_consumer_key="0685bd9184jfhq22",
oauth_token="ad180jjd733klru7",
oauth_signature_method="HMAC-SHA1",
oauth_signature="wOJIO9A2W5mFwDgiDvZbTSMK%2FPY%3D",
oauth_timestamp="137131200",
oauth_nonce="4572616e48616d6d65724c61686176",
oauth_version="1.0"
Protocol parameters SHALL be included in the "Authorization" header
as follows:
1. Parameter names and values are encoded per Parameter Encoding
(Section 3.6).
2. Each parameter's name is immediately followed by an "=" character
(ASCII code 61), a """ character (ASCII code 34), the parameter
value (MAY be empty), and another """ character (ASCII code 34).
3. Parameters are separated by a "," character (ASCII code 44) and
OPTIONAL linear whitespace per [RFC2617].
4. The OPTIONAL "realm" parameter MAY be added and interpreted per
[RFC2617], section 1.2.
Servers MAY indicate their support for the "OAuth" auth-scheme by
returning the HTTP "WWW-Authenticate" response header upon client
requests for protected resources. As per [RFC2617] such a response
MAY include additional HTTP "WWW-Authenticate" headers:
For example:
WWW-Authenticate: OAuth realm="http://server.example.com/"
The realm parameter defines a protection realm per [RFC2617], section
1.2.
3.4.2. Form-Encoded Body
Protocol parameters can be transmitted in the HTTP request entity-
body, but only if the following REQUIRED conditions are met:
o The entity-body is single-part.
o The entity-body follows the encoding requirements of the
"application/x-www-form-urlencoded" content-type as defined by
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[W3C.REC-html40-19980424].
o The HTTP request entity-header includes the "Content-Type" header
set to "application/x-www-form-urlencoded".
For example (line breaks are for display purposes only):
oauth_consumer_key=0685bd9184jfhq22&oauth_token=ad180jjd733klr
u7&oauth_signature_method=HMAC-SHA1&oauth_signature=wOJIO9A2W5
mFwDgiDvZbTSMK%2FPY%3D&oauth_timestamp=137131200&oauth_nonce=4
572616e48616d6d65724c61686176&oauth_version=1.0
The entity-body MAY include other request-specific parameters, in
which case, the protocol parameters SHOULD be appended following the
request-specific parameters, properly separated by an "&" character
(ASCII code 38).
3.4.3. Request URI Query
Protocol parameters can be transmitted by being added to the HTTP
request URI as a query parameter as defined by [RFC3986] section 3.
For example (line breaks are for display purposes only):
GET /example/path?oauth_consumer_key=0685bd9184jfhq22&
oauth_token=ad180jjd733klru7&oauth_signature_method=HM
AC-SHA1&oauth_signature=wOJIO9A2W5mFwDgiDvZbTSMK%2FPY%
3D&oauth_timestamp=137131200&oauth_nonce=4572616e48616
d6d65724c61686176&oauth_version=1.0 HTTP/1.1
The request URI MAY include other request-specific query parameters,
in which case, the protocol parameters SHOULD be appended following
the request-specific parameters, properly separated by an "&"
character (ASCII code 38).
3.5. Server Response
Servers receiving an authenticated request MUST:
o Recalculate the request signature independently and compare it to
the value received from the client.
o Ensure that the nonce / timestamp / token combination has not been
used before, and MAY reject requests with stale timestamps.
o If a token is present, verify the scope and status of the client
authorization by using the token, and MAY choose to restrict token
usage to the client to which it was issued.
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o Ensure that the protocol version used is "1.0".
If the request fails verification, the server SHOULD respond with the
appropriate HTTP response status code. The server MAY include
further details about why the request was rejected in the response
body. The following status codes SHOULD be used:
o 400 (Bad Request)
* Unsupported parameters
* Unsupported signature method
* Missing parameters
* Duplicated protocol parameters
o 401 (Unauthorized)
* Invalid client credentials
* Invalid or expired token
* Invalid signature
* Invalid or used nonce
3.6. Percent Encoding
OAuth uses the following percent-encoding rules:
1. Text values are first encoded as UTF-8 octets per [RFC3629] if
they are not already. This does not include binary values which
are not intended for human consumption.
2. The values are then escaped using the [RFC3986] percent-encoding
(%XX) mechanism as follows:
* Characters in the unreserved character set as defined by
[RFC3986] section 2.3 (ALPHA, DIGIT, "-", ".", "_", "~") MUST
NOT be encoded.
* All other characters MUST be encoded.
* The two hexadecimal characters use to represent encoded
characters MUST be upper case.
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4. IANA Considerations
This memo includes no request to IANA.
5. Security Considerations
As stated in [RFC2617], the greatest sources of risks are usually
found not in the core protocol itself but in policies and procedures
surrounding its use. Implementers are strongly encouraged to assess
how this protocol addresses their security requirements.
5.1. RSA-SHA1 Signature Method
When used with "RSA-SHA1" signatures, the OAuth protocol does not use
the token shared-secret, or any provisioned client shared-secret.
This means the protocol relies completely on the secrecy of the
private key used by the client to sign requests.
5.2. PLAINTEXT Signature Method
When used with the "PLAINTEXT" method, the protocol makes no attempts
to protect credentials from eavesdroppers or man-in-the-middle
attacks. The "PLAINTEXT" method is only intended to be used in
conjunction with a transport-layer security mechanism such as TLS or
SSL which does provide such protection.
5.3. Confidentiality of Requests
While OAuth provides a mechanism for verifying the integrity of
requests, it provides no guarantee of request confidentiality.
Unless further precautions are taken, eavesdroppers will have full
access to request content. Servers should carefully consider the
kinds of data likely to be sent as part of such requests, and should
employ transport-layer security mechanisms to protect sensitive
resources.
5.4. Spoofing by Counterfeit Servers
OAuth makes no attempt to verify the authenticity of the server. A
hostile party could take advantage of this by intercepting the
client's requests and returning misleading or otherwise incorrect
responses. Service providers should consider such attacks when
developing services based on OAuth, and should require transport-
layer security for any requests where the authenticity of the server
or of request responses is an issue.
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5.5. Proxying and Caching of Authenticated Content
The HTTP Authorization scheme (Section 3.4.1) is optional. However,
[RFC2616] relies on the "Authorization" and "WWW-Authenticate"
headers to distinguish authenticated content so that it can be
protected. Proxies and caches, in particular, may fail to adequately
protect requests not using these headers.
For example, private authenticated content may be stored in (and thus
retrievable from) publicly-accessible caches. Servers not using the
HTTP Authorization header (Section 3.4.1) should take care to use
other mechanisms, such as the "Cache-Control" header, to ensure that
authenticated content is protected.
5.6. Plaintext Storage of Credentials
The client shared-secret and token shared-secret function the same
way passwords do in traditional authentication systems. In order to
compute the signatures used in methods other than "RSA-SHA1", the
server must have access to these secrets in plaintext form. This is
in contrast, for example, to modern operating systems, which store
only a one-way hash of user credentials.
If an attacker were to gain access to these secrets - or worse, to
the server's database of all such secrets - he or she would be able
to perform any action on behalf of any resource owner. Accordingly,
it is critical that servers protect these secrets from unauthorized
access.
5.7. Secrecy of the Client Credentials
In many cases, the client application will be under the control of
potentially untrusted parties. For example, if the client is a
freely available desktop application, an attacker may be able to
download a copy for analysis. In such cases, attackers will be able
to recover the client credentials.
Accordingly, servers should not use the client credentials alone to
verify the identity of the client. Where possible, other factors
such as IP address should be used as well.
5.8. Cryptographic Attacks
SHA-1, the hash algorithm used in "HMAC-SHA1" signatures, has been
shown [SHA1-CHARACTERISTICS] to have a number of cryptographic
weaknesses that significantly reduce its resistance to collision
attacks. Practically speaking, these weaknesses are difficult to
exploit, and by themselves do not pose a significant risk to users of
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OAuth. They may, however, make more efficient attacks possible, and
NIST has announced [SHA-COMMENTS] that it will phase out use of SHA-1
by 2010. Servers should take this into account when considering
whether SHA-1 provides an adequate level of security for their
applications.
5.9. Signature Base String Limitations
The signature base string has been designed to support the signature
methods defined in this specification. When designing additional
signature methods, the signature base string should be evaluated to
ensure compatibility with the algorithms used.
Since the signature base string does not cover the entire HTTP
request, such as most request entity-body, most entity-headers, and
the order in which parameters are sent, servers should employ
additional mechanisms to protect such elements.
Appendix A. Examples
[[ TODO ]]
Appendix B. Acknowledgments
This specification is directly based on the [OAuth Core 1.0 Revision
A] community specification which was the product of the OAuth
community. OAuth was modeled after existing proprietary protocols
and best practices that have been independently implemented by
various web sites. This specification was orignially authored by:
Mark Atwood, Richard M. Conlan, Blaine Cook, Leah Culver, Kellan
Elliott-McCrea, Larry Halff, Eran Hammer-Lahav, Ben Laurie, Chris
Messina, John Panzer, Sam Quigley, David Recordon, Eran Sandler,
Jonathan Sergent, Todd Sieling, Brian Slesinsky, and Andy Smith
Appendix C. Document History
[[ To be removed by the RFC editor before publication as an RFC. ]]
-00
o Transitioned from the individual submission draft-hammer-oauth-02
to working group draft.
o Split draft-hammer-oauth-02 into two drafts, one dealing with
authentication (this draft) and another dealing with web
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delegation draft-ietf-oauth-web-delegation.
6. References
6.1. Normative References
[RFC2045] Freed, N. and N. Borenstein, "Multipurpose Internet Mail
Extensions (MIME) Part One: Format of Internet Message
Bodies", RFC 2045, November 1996.
[RFC2104] Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
Hashing for Message Authentication", RFC 2104,
February 1997.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2616] Fielding, R., Gettys, J., Mogul, J., Frystyk, H.,
Masinter, L., Leach, P., and T. Berners-Lee, "Hypertext
Transfer Protocol -- HTTP/1.1", RFC 2616, June 1999.
[RFC2617] Franks, J., Hallam-Baker, P., Hostetler, J., Lawrence, S.,
Leach, P., Luotonen, A., and L. Stewart, "HTTP
Authentication: Basic and Digest Access Authentication",
RFC 2617, June 1999.
[RFC3447] Jonsson, J. and B. Kaliski, "Public-Key Cryptography
Standards (PKCS) #1: RSA Cryptography Specifications
Version 2.1", RFC 3447, February 2003.
[RFC3629] Yergeau, F., "UTF-8, a transformation format of ISO
10646", STD 63, RFC 3629, November 2003.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, January 2005.
[W3C.REC-html40-19980424]
Hors, A., Jacobs, I., and D. Raggett, "HTML 4.0
Specification", World Wide Web Consortium
Recommendation REC-html40-19980424, April 1998,
<http://www.w3.org/TR/1998/REC-html40-19980424>.
[draft-ietf-oauth-web-delegation]
Hammer-Lahav, E., Ed., "The OAuth Protocol: Web
Delegation".
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6.2. Informative References
[OAuth Core 1.0 Revision A]
OAuth, OCW., "OAuth Core 1.0".
[]
National Institute of Standards and Technology, NIST.,
"NIST Brief Comments on Recent Cryptanalytic Attacks on
Secure Hashing Functions and the Continued Security
Provided by SHA-1, August, 2004.".
[SHA1-CHARACTERISTICS]
De Canniere, C. and C. Rechberger, "Finding SHA-1
Characteristics: General Results and Applications".
Author's Address
Eran Hammer-Lahav (editor)
Yahoo!
Email: eran@hueniverse.com
URI: http://hueniverse.com
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