rfc7662.xml

<?xml version="1.0" encoding="US-ASCII"?>
<!DOCTYPE rfc SYSTEM "rfc2629.dtd">
<?rfc toc="yes"?>
<?rfc tocompact="yes"?>
<?rfc tocdepth="3"?>
<?rfc tocindent="yes"?>
<?rfc symrefs="yes"?>
<?rfc sortrefs="yes"?>
<?rfc comments="yes"?>
<?rfc inline="yes"?>
<?rfc compact="yes"?>
<?rfc subcompact="no"?>
<rfc category="std" consensus="yes" ipr="trust200902" number="7662"
     submissionType="IETF">
  <front>
    <title abbrev="OAuth Introspection">OAuth 2.0 Token Introspection</title>

    <author fullname="Justin Richer" initials="J." role="editor"
            surname="Richer">
      <organization/>

      <address>
        <email>ietf@justin.richer.org</email>
      </address>
    </author>

    <date month="October" year="2015"/>

    <area>Security</area>

    <workgroup>OAuth Working Group</workgroup>

    <!-- [rfced] Please insert any keywords (beyond those that appear in 
the title) for use on http://www.rfc-editor.org/search.


[justin] done.-->

    <keyword>token validation</keyword>

    <keyword>oauth token validation</keyword>

    <keyword>active token</keyword>

    <keyword>inactive token</keyword>

    <keyword>token metadata</keyword>

    <keyword>token status</keyword>

    <keyword>token status check</keyword>

    <abstract>
      <t>This specification defines a method for a protected resource to query
      an OAuth 2.0 authorization server to determine the active state of an
      OAuth 2.0 token and to determine meta-information about this token.
      OAuth 2.0 deployments can use this method to convey information about
      the authorization context of the token from the authorization server to
      the protected resource.</t>
    </abstract>
  </front>

  <middle>
    <section anchor="introduction" title="Introduction">
      <t>In <xref target="RFC6749"> OAuth 2.0</xref>, the contents of tokens
      are opaque to clients. This means that the client does not need to know
      anything about the content or structure of the token itself, if there is
      any. However, there is still a large amount of metadata that may be
      attached to a token, such as its current validity, approved scopes, and
      information about the context in which the token was issued. These
      pieces of information are often vital to protected resources making
      authorization decisions based on the tokens being presented. Since OAuth
      2.0 does not define a protocol for the resource server to learn
      meta-information about a token that it has received from an
      authorization server, several different approaches have been developed
      to bridge this gap. These include using structured token formats such as
      <xref target="RFC7519">JWT</xref> or proprietary inter-service
      communication mechanisms (such as shared databases and protected
      enterprise service buses) that convey token information.</t>

      <t>This specification defines a protocol that allows authorized
      protected resources to query the authorization server to determine the
      set of metadata for a given token that was presented to them by an OAuth
      2.0 client. This metadata includes whether or not the token is currently
      active (or if it has expired or otherwise been revoked), what rights of
      access the token carries (usually conveyed through OAuth 2.0 scopes),
      and the authorization context in which the token was granted (including
      who authorized the token and which client it was issued to). Token
      introspection allows a protected resource to query this information
      regardless of whether or not it is carried in the token itself, allowing
      this method to be used along with or independently of structured token
      values. Additionally, a protected resource can use the mechanism
      described in this specification to introspect the token in a particular
      authorization decision context and ascertain the relevant metadata about
      the token to make this authorization decision appropriately.</t>

      <section anchor="Notation" title="Notational Conventions">
        <t>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
        <xref target="RFC2119"/>.</t>

        <t>Unless otherwise noted, all the protocol parameter names and values
        are case sensitive.</t>
      </section>

      <section title="Terminology">
        <t>This section defines the terminology used by this specification.
        This section is a normative portion of this specification, imposing
        requirements upon implementations.</t>

        <t>This specification uses the terms "access token", "authorization
        endpoint", "authorization grant", "authorization server", "client",
        "client identifier", "protected resource", "refresh token", "resource
        owner", "resource server", and "token endpoint" defined by <xref
        target="RFC6749">OAuth 2.0</xref>, and the terms "claim names" and
        "claim values" defined by <xref target="RFC7519">JSON Web Token
        (JWT)</xref>.</t>

        <t>This specification defines the following terms:</t>

        <t>
          <list style="hanging">
            <t hangText="Token Introspection"><vspace/>The act of inquiring
            about the current state of an OAuth 2.0 token through use of the
            network protocol defined in this document.</t>

            <t hangText="Introspection Endpoint"><vspace/>The OAuth 2.0
            endpoint through which the token introspection operation is
            accomplished.</t>
          </list>
        </t>
      </section>
    </section>

    <section anchor="IntrospectionEndpoint" title="Introspection Endpoint">
      <t hangText="instance_name">The introspection endpoint is an OAuth 2.0
      endpoint that takes a parameter representing an OAuth 2.0 token and
      returns a <xref target="RFC7159">JSON</xref> document representing the
      meta information surrounding the token, including whether this token is
      currently active. The definition of an active token is dependent upon
      the authorization server, but this is commonly a token that has been
      issued by this authorization server, is not expired, has not been
      revoked, and is valid for use at the protected resource making the
      introspection call.</t>

      <t hangText="instance_name">The introspection endpoint MUST be protected
      by a transport-layer security mechanism as described in <xref
      target="Security"/>. The means by which the protected resource discovers
      the location of the introspection endpoint are outside the scope of this
      specification.</t>

      <section anchor="IntrospectionRequest" title="Introspection Request">
        <t hangText="instance_name">The protected resource calls the
        introspection endpoint using an <xref target="RFC7231">HTTP
        POST</xref> request with parameters sent as <spanx
        style="verb">application/x-www-form-urlencoded</spanx> data as defined
        in <xref target="W3C.REC-html5-20141028"/>. The protected resource
        sends a parameter representing the token along with optional
        parameters representing additional context that is known by the
        protected resource to aid the authorization server in its
        response.</t>

        <t hangText="instance_name">
          <list style="hanging">
            <t hangText="token"><vspace/>REQUIRED. The string value of the
            token. For access tokens, this is the <spanx
            style="verb">access_token</spanx> value returned from the token
            endpoint defined in <xref target="RFC6749">OAuth 2.0</xref>,
            Section 5.1. For refresh tokens, this is the <spanx
            style="verb">refresh_token</spanx> value returned from the token
            endpoint as defined in <xref target="RFC6749">OAuth 2.0</xref>,
            Section 5.1. Other token types are outside the scope of this
            specification.</t>

            <t hangText="token_type_hint"><vspace/>OPTIONAL. A hint about the
            type of the token submitted for introspection. The protected
            resource MAY pass this parameter to help the authorization server
            optimize the token lookup. If the server is unable to locate the
            token using the given hint, it MUST extend its search across all
            of its supported token types. An authorization server MAY ignore
            this parameter, particularly if it is able to detect the token
            type automatically. Values for this field are defined in the
            "OAuth Token Type Hints" registry defined in <xref
            target="RFC7009">OAuth Token Revocation</xref>.</t>
          </list>
        </t>

        <t hangText="instance_name">The introspection endpoint MAY accept
        other OPTIONAL parameters to provide further context to the query. For
        instance, an authorization server may desire to know the IP address of
        the client accessing the protected resource to determine if the
        correct client is likely to be presenting the token. The definition of
        this or any other parameters are outside the scope of this
        specification, to be defined by service documentation or extensions to
        this specification. If the authorization server is unable to determine
        the state of the token without additional information, it SHOULD
        return an introspection response indicating the token is not active as
        described in <xref target="IntrospectionResponse"/>.</t>

        <t hangText="instance_name">To prevent token scanning attacks, the
        endpoint MUST also require some form of authorization to access this
        endpoint, such as client authentication as described in <xref
        target="RFC6749">OAuth 2.0</xref> or a separate OAuth 2.0 access token
        such as the bearer token described in <xref target="RFC6750">OAuth 2.0
        Bearer Token Usage</xref>. The methods of managing and validating
        these authentication credentials are out of scope of this
        specification.</t>

        <t>For example, the following shows a protected resource calling the
        token introspection endpoint to query about an OAuth 2.0 bearer token.
        The protected resource is using a separate OAuth 2.0 bearer token to
        authorize this call.</t>

        <figure>
          <preamble>The following is a non-normative example
          request:</preamble>

          <artwork><![CDATA[
  POST /introspect HTTP/1.1
  Host: server.example.com
  Accept: application/json
  Content-Type: application/x-www-form-urlencoded
  Authorization: Bearer 23410913-abewfq.123483

  token=2YotnFZFEjr1zCsicMWpAA

]]></artwork>
        </figure>

        <t>In this example, the protected resource uses a client identifier
        and client secret to authenticate itself to the introspection
        endpoint. The protected resource also sends a token type hint
        indicating that it is inquiring about an access token.</t>

        <figure>
          <preamble>The following is a non-normative example
          request:</preamble>

          <artwork><![CDATA[
  POST /introspect HTTP/1.1
  Host: server.example.com
  Accept: application/json
  Content-Type: application/x-www-form-urlencoded
  Authorization: Basic czZCaGRSa3F0MzpnWDFmQmF0M2JW

  token=mF_9.B5f-4.1JqM&token_type_hint=access_token

]]></artwork>
        </figure>
      </section>

      <section anchor="IntrospectionResponse" title="Introspection Response">
        <t>The server responds with a <xref target="RFC7159">JSON
        object</xref> in <spanx style="verb">application/json</spanx> format
        with the following top-level members.</t>

        <t>
          <list style="hanging">
            <t hangText="active"><vspace/>REQUIRED. Boolean indicator of
            whether or not the presented token is currently active. The
            specifics of a token&rsquo;s <spanx style="verb">active</spanx>
            state will vary depending on the implementation of the
            authorization server and the information it keeps about its
            tokens, but a <spanx style="verb">true</spanx> value return for
            the <spanx style="verb">active</spanx> property will generally
            indicate that a given token has been issued by this authorization
            server, has not been revoked by the resource owner, and is within
            its given time window of validity (e.g., after its issuance time
            and before its expiration time). See <xref target="Security"/> for
            information on implementation of such checks.</t>

            <t hangText="scope"><vspace/>OPTIONAL. A JSON string containing a
            space-separated list of scopes associated with this token, in the
            format described in Section 3.3 of <xref target="RFC6749">OAuth
            2.0</xref>.</t>

            <t hangText="client_id"><vspace/>OPTIONAL. Client identifier for
            the OAuth 2.0 client that requested this token.</t>

            <t hangText="username"><vspace/>OPTIONAL. Human-readable
            identifier for the resource owner who authorized this token.</t>

            <t hangText="token_type"><vspace/>OPTIONAL. Type of the token as
            defined in Section 5.1 of <xref target="RFC6749">OAuth
            2.0</xref>.</t>

            <t hangText="exp"><vspace/>OPTIONAL. Integer timestamp, measured
            in the number of seconds since January 1 1970 UTC, indicating when
            this token will expire, as defined in <xref
            target="RFC7519">JWT</xref>.</t>

            <t hangText="iat"><vspace/>OPTIONAL. Integer timestamp, measured
            in the number of seconds since January 1 1970 UTC, indicating when
            this token was originally issued, as defined in <xref
            target="RFC7519">JWT</xref>.</t>

            <t hangText="nbf"><vspace/>OPTIONAL. Integer timestamp, measured
            in the number of seconds since January 1 1970 UTC, indicating when
            this token is not to be used before, as defined in <xref
            target="RFC7519">JWT</xref>.</t>

            <t hangText="sub"><vspace/>OPTIONAL. Subject of the token, as
            defined in <xref target="RFC7519">JWT</xref>. Usually a
            machine-readable identifier of the resource owner who authorized
            this token.</t>

            <t hangText="aud"><vspace/>OPTIONAL. Service-specific string
            identifier or list of string identifiers representing the intended
            audience for this token, as defined in <xref
            target="RFC7519">JWT</xref>.</t>

            <t hangText="iss"><vspace/>OPTIONAL. String representing the
            issuer of this token, as defined in <xref
            target="RFC7519">JWT</xref>.</t>

            <t hangText="jti"><vspace/>OPTIONAL. String identifier for the
            token, as defined in <xref target="RFC7519">JWT</xref>.</t>
          </list>
        </t>

        <t>Specific implementations MAY extend this structure with their own
        service-specific response names as top-level members of this JSON
        object. Response names intended to be used across domains MUST be
        registered in the "OAuth Token Introspection Response" registry
        defined in <xref target="IntrospectionResponseRegistry"/>.</t>

        <t>The authorization server MAY respond differently to different
        protected resources making the same request. For instance, an
        authorization server MAY limit which scopes from a given token are
        returned for each protected resource to prevent a protected resource
        from learning more about the larger network than is necessary for its
        operation.</t>

        <t>The response MAY be cached by the protected resource to improve
        performance and reduce load on the introspection endpoint, but at the
        cost of liveness of the information used by the protected resource to
        make authorization decisions. See <xref target="Security"/> for more
        information regarding the trade off when the response is cached.</t>

        <t>For example, the following response contains a set of information
        about an active token:</t>

        <figure>
          <preamble>The following is a non-normative example
          response:</preamble>

          <artwork><![CDATA[
  HTTP/1.1 200 OK
  Content-Type: application/json

  {
   "active": true,
   "client_id": "l238j323ds-23ij4",
   "username": "jdoe",
   "scope": "read write dolphin",
   "sub": "Z5O3upPC88QrAjx00dis",
   "aud": "https://protected.example.net/resource",
   "iss": "https://server.example.com/",
   "exp": 1419356238,
   "iat": 1419350238,
   "extension_field": "twenty-seven"
  }

]]></artwork>
        </figure>

        <t/>

        <t>If the introspection call is properly authorized but the token is
        not active, does not exist on this server, or the protected resource
        is not allowed to introspect this particular token, then the
        authorization server MUST return an introspection response with the
        <spanx style="verb">active</spanx> field set to <spanx
        style="verb">false</spanx>. Note that to avoid disclosing too much of
        the authorization server's state to a third party, the authorization
        server SHOULD NOT include any additional information about an inactive
        token, including why the token is inactive.</t>

        <figure>
          <preamble>The following is a non-normative example response for a
          token that has been revoked or is otherwise invalid:</preamble>

          <artwork><![CDATA[
  HTTP/1.1 200 OK
  Content-Type: application/json

  {
   "active": false
  }

]]></artwork>
        </figure>
      </section>

      <section anchor="ErrorResponse" title="Error Response">
        <t>If the protected resource uses OAuth 2.0 client credentials to
        authenticate to the introspection endpoint and its credentials are
        invalid, the authorization server responds with an HTTP 401
        (Unauthorized) as described in Section 5.2 of <xref
        target="RFC6749">OAuth 2.0 </xref>.</t>

        <t>If the protected resource uses an OAuth 2.0 bearer token to
        authorize its call to the introspection endpoint and the token used
        for authorization does not contain sufficient privileges or is
        otherwise invalid for this request, the authorization server responds
        with an HTTP 401 code as described in Section 3 of <xref
        target="RFC6750">OAuth 2.0 Bearer Token Usage</xref>.</t>

        <t>Note that a properly formed and authorized query for an inactive or
        otherwise invalid token (or a token the protected resource is not
        allowed to know about) is not considered an error response by this
        specification. In these cases, the authorization server MUST instead
        respond with an introspection response with the <spanx
        style="verb">active</spanx> field set to <spanx
        style="verb">false</spanx> as described in <xref
        target="IntrospectionResponse"/>.</t>
      </section>
    </section>

    <section anchor="IANA" title="IANA Considerations">
      <section anchor="IntrospectionResponseRegistry"
               title="OAuth Token Introspection Response Registry">
        <t>This specification establishes the "OAuth Token Introspection
        Response" registry.</t>

        <t>OAuth registration client metadata names and descriptions are
        registered by Specification Required <xref target="RFC5226"/> after a
        two-week review period on the oauth-ext-review@ietf.org mailing list,
        on the advice of one or more Designated Experts. However, to allow for
        the allocation of names prior to publication, the Designated Expert(s)
        may approve registration once they are satisfied that such a
        specification will be published.</t>

        <t>Registration requests sent to the mailing list for review should
        use an appropriate subject (e.g., "Request to register OAuth Token
        Introspection Response name: example").</t>

        <t>Within the review period, the Designated Expert(s) will either
        approve or deny the registration request, communicating this decision
        to the review list and IANA. Denials should include an explanation
        and, if applicable, suggestions as to how to make the request
        successful.</t>

        <t>IANA must only accept registry updates from the Designated
        Expert(s) and should direct all requests for registration to the
        review mailing list.</t>

        <section anchor="MetadataTemplate" title="Registration Template">
          <t>
            <list style="hanging">
              <t hangText="Name:"><vspace/> The name requested (e.g.,
              "example"). This name is case sensitive. Names that match other
              registered names in a case insensitive manner SHOULD NOT be
              accepted. Names that match claims registered in the "JSON Web
              Token Claims" registry established by <xref target="RFC7519"/>
              SHOULD have comparable definitions and semantics.</t>

              <t hangText="Description:"><vspace/> Brief description of the
              metadata value (e.g., "Example description").</t>

              <t hangText="Change controller:"><vspace/> For Standards Track
              RFCs, state "IESG". For other documents, give the name of the
              responsible party. Other details (e.g., postal address, email
              address, home page URI) may also be included.</t>

              <t hangText="Specification document(s):"><vspace/> Reference to
              the document(s) that specify the token endpoint authorization
              method, preferably including a URI that can be used to retrieve
              a copy of the document(s). An indication of the relevant
              sections may also be included but is not required.</t>
            </list>
          </t>
        </section>

        <section anchor="MetadataContents" title="Initial Registry Contents">
          <t>The initial contents of the "OAuth Token Introspection Response"
          registry are as follows:</t>

          <t>
            <?rfc subcompact="yes"?>

            <list style="symbols">
              <t>Name: <spanx style="verb">active</spanx></t>

              <t>Description: Token active status</t>

              <t>Change Controller: IESG</t>

              <t>Specification Document(s): <xref
              target="IntrospectionResponse"/> of RFC 7662 (this
              document).</t>
            </list>

            <list style="symbols">
              <t>Name: <spanx style="verb">username</spanx></t>

              <t>Description: User identifier of the resource owner</t>

              <t>Change Controller: IESG</t>

              <t>Specification Document(s): <xref
              target="IntrospectionResponse"/> of RFC 7662 (this
              document).</t>
            </list>

            <list style="symbols">
              <t>Name: <spanx style="verb">client_id</spanx></t>

              <t>Description: Client identifier of the client</t>

              <t>Change Controller: IESG</t>

              <t>Specification Document(s): <xref
              target="IntrospectionResponse"/> of RFC 7662 (this
              document).</t>
            </list>

            <list style="symbols">
              <t>Name: <spanx style="verb">scope</spanx></t>

              <t>Description: Authorized scopes of the token</t>

              <t>Change Controller: IESG</t>

              <t>Specification Document(s): <xref
              target="IntrospectionResponse"/> of RFC 7662 (this
              document).</t>
            </list>

            <list style="symbols">
              <t>Name: <spanx style="verb">token_type</spanx></t>

              <t>Description: Type of the token</t>

              <t>Change Controller: IESG</t>

              <t>Specification Document(s): <xref
              target="IntrospectionResponse"/> of RFC 7662 (this
              document).</t>
            </list>
          </t>

          <t>
            <list style="symbols">
              <t>Name: <spanx style="verb">exp</spanx></t>

              <t>Description: Expiration timestamp of the token</t>

              <t>Change Controller: IESG</t>

              <t>Specification Document(s): <xref
              target="IntrospectionResponse"/> of RFC 7662 (this
              document).</t>
            </list>

            <list style="symbols">
              <t>Name: <spanx style="verb">iat</spanx></t>

              <t>Description: Issuance timestamp of the token</t>

              <t>Change Controller: IESG</t>

              <t>Specification Document(s): <xref
              target="IntrospectionResponse"/> of RFC 7662 (this
              document).</t>
            </list>

            <list style="symbols">
              <t>Name: <spanx style="verb">nbf</spanx></t>

              <t>Description: Timestamp before which the token is not
              valid</t>

              <t>Change Controller: IESG</t>

              <t>Specification Document(s): <xref
              target="IntrospectionResponse"/> of RFC 7662 (this
              document).</t>
            </list>

            <list style="symbols">
              <t>Name: <spanx style="verb">sub</spanx></t>

              <t>Description: Subject of the token</t>

              <t>Change Controller: IESG</t>

              <t>Specification Document(s): <xref
              target="IntrospectionResponse"/> of RFC 7662 (this
              document).</t>
            </list>

            <list style="symbols">
              <t>Name: <spanx style="verb">aud</spanx></t>

              <t>Description: Audience of the token</t>

              <t>Change Controller: IESG</t>

              <t>Specification Document(s): <xref
              target="IntrospectionResponse"/> of RFC 7662 (this
              document).</t>
            </list>

            <list style="symbols">
              <t>Name: <spanx style="verb">iss</spanx></t>

              <t>Description: Issuer of the token</t>

              <t>Change Controller: IESG</t>

              <t>Specification Document(s): <xref
              target="IntrospectionResponse"/> of RFC 7662 (this
              document).</t>
            </list>

            <list style="symbols">
              <t>Name: <spanx style="verb">jti</spanx></t>

              <t>Description: Unique identifier of the token</t>

              <t>Change Controller: IESG</t>

              <t>Specification Document(s): <xref
              target="IntrospectionResponse"/> of RFC 7662 (this
              document).</t>
            </list>
          </t>
        </section>

        <?rfc subcompact="no"?>
      </section>
    </section>

    <section anchor="Security" title="Security Considerations">
      <t>Since there are many different and valid ways to implement an OAuth
      2.0 system, there are consequently many ways for an authorization server
      to determine whether or not a token is currently <spanx
      style="verb">active</spanx>. However, since resource servers using token
      introspection rely on the authorization server to determine the state of
      a token, the authorization server MUST perform all applicable checks
      against a token's state. For instance, these tests include the
      following: <list style="symbols">
          <t>If the token can expire, the authorization server MUST determine
          whether or not the token has expired.</t>

          <t>If the token can be issued before it is able to be used, the
          authorization server MUST determine whether or not a token's valid
          period has started yet.</t>

          <t>If the token can be revoked after it was issued, the
          authorization server MUST determine whether or not such a revocation
          has taken place.</t>

          <t>If the token has been signed, the authorization server MUST
          validate the signature.</t>

          <t>If the token can be used only at certain resource servers, the
          authorization server MUST determine whether or not the token can be
          used at the resource server making the introspection call.</t>
        </list></t>

      <t>If an authorization server fails to perform any applicable check, the
      resource server could make an erroneous security decision based on that
      response. Note that not all of these checks will be applicable to all
      OAuth 2.0 deployments and it is up to the authorization server to
      determine which of these checks (and any other checks) apply.</t>

      <t>If left unprotected and un-throttled, the introspection endpoint
      could present a means for an attacker to poll a series of possible token
      values, fishing for a valid token. To prevent this, the authorization
      server MUST require authentication of protected resources that need to
      access the introspection endpoint and SHOULD require protected resources
      to be specifically authorized to call the introspection endpoint. The
      specifics of such authentication credentials are out of scope of this
      specification, but commonly these credentials could take the form of any
      valid client authentication mechanism used with the token endpoint, an
      OAuth 2.0 access token, or other HTTP authorization or authentication
      mechanism. A single piece of software acting as both a client and a
      protected resource MAY reuse the same credentials between the token
      endpoint and the introspection endpoint, though doing so potentially
      conflates the activities of the client and protected resource portions
      of the software and the authorization server MAY require separate
      credentials for each mode.</t>

      <t>Since the introspection endpoint takes in OAuth 2.0 tokens as
      parameters and responds with information used to make authorization
      decisions, the server MUST support Transport Layer Security (TLS) 1.2
      <xref target="RFC5246"/> and MAY support additional transport-layer
      mechanisms meeting its security requirements. When using TLS, the client
      or protected resource MUST perform a TLS/SSL server certificate check,
      as specified in <xref target="RFC6125"/>. Implementation security
      considerations can be found in <xref target="BCP195">Recommendations for
      Secure Use of TLS and DTLS</xref>.</t>

      <t>To prevent the values of access tokens from leaking into server-side
      logs via query parameters, an authorization server offering token
      introspection MAY disallow the use of HTTP GET on the introspection
      endpoint and instead require the HTTP POST method to be used at the
      introspection endpoint.</t>

      <t>To avoid disclosing the internal state of the authorization server,
      an introspection response for an inactive token SHOULD NOT contain any
      additional claims beyond the required <spanx style="verb">active</spanx>
      claim (with its value set to <spanx style="verb">false</spanx>).</t>

      <t>Since a protected resource MAY cache the response of the
      introspection endpoint, designers of an OAuth 2.0 system using this
      protocol MUST consider the performance and security trade-offs inherent
      in caching security information such as this. A less aggressive cache
      with a short timeout will provide the protected resource with more
      up-to-date information (due to it needing to query the introspection
      endpoint more often) at the cost of increased network traffic and load
      on the introspection endpoint. A more aggressive cache with a longer
      duration will minimize network traffic and load on the introspection
      endpoint, but at the risk of stale information about the token. For
      example, the token may be revoked while the protected resource is
      relying on the value of the cached response to make authorization
      decisions. This creates a window during which a revoked token could be
      used at the protected resource. Consequently, an acceptable cache
      validity duration needs to be carefully considered given the concerns
      and sensitivities of the protected resource being accessed and the
      likelihood of a token being revoked or invalidated in the interim
      period. Highly sensitive environments can opt to disable caching
      entirely on the protected resource to eliminate the risk of stale cached
      information entirely, again at the cost of increased network traffic and
      server load. If the response contains the <spanx
      style="verb">exp</spanx> parameter (expiration), the response MUST NOT
      be cached beyond the time indicated therein.</t>

      <t>An authorization server offering token introspection must be able to
      understand the token values being presented to it during this call. The
      exact means by which this happens is an implementation detail and is
      outside the scope of this specification. For unstructured tokens, this
      could take the form of a simple server-side database query against a
      data store containing the context information for the token. For
      structured tokens, this could take the form of the server parsing the
      token, validating its signature or other protection mechanisms, and
      returning the information contained in the token back to the protected
      resource (allowing the protected resource to be unaware of the token's
      contents, much like the client). Note that for tokens carrying encrypted
      information that is needed during the introspection process, the
      authorization server must be able to decrypt and validate the token to
      access this information. Also note that in cases where the authorization
      server stores no information about the token and has no means of
      accessing information about the token by parsing the token itself, it
      cannot likely offer an introspection service.</t>
    </section>

    <section anchor="Privacy" title="Privacy Considerations">
      <t>The introspection response may contain privacy-sensitive information
      such as user identifiers for resource owners. When this is the case,
      measures MUST be taken to prevent disclosure of this information to
      unintended parties. One method is to transmit user identifiers as opaque
      service-specific strings, potentially returning different identifiers to
      each protected resource.</t>

      <t>If the protected resource sends additional information about the
      client's request to the authorization server (such as the client's IP
      address) using an extension of this specification, such information
      could have additional privacy considerations that the extension should
      detail. However, the nature and implications of such extensions are
      outside the scope of this specification.</t>

      <t>Omitting privacy-sensitive information from an introspection response
      is the simplest way of minimizing privacy issues.</t>
    </section>
  </middle>

  <back>
    <references title="Normative References">
      <?rfc include="reference.RFC.2119"?>

      <?rfc include="reference.RFC.5226"?>

      <?rfc include="reference.RFC.5246"?>

      <?rfc include="reference.RFC.6125"?>

      <?rfc include="reference.RFC.6749"?>

      <?rfc include="reference.RFC.6750"?>

      <?rfc include="reference.RFC.7009"?>

      <?rfc include="reference.RFC.7159"?>

      <?rfc include="reference.RFC.7231"?>

      <?rfc include="reference.RFC.7519"?>

      <?rfc include='http://xml2rfc.ietf.org/public/rfc/bibxml4/reference.W3C.REC-html5-20141028.xml'?>
    </references>

    <references title="Informative References">
      <!-- [rfced] [TLS-BCP] has been published as RFC 7525.  The reference entry
has been updated accordignly.  Please let us know any objections. 

[ Justin ] I've replaced the reference with the final BCP reference instead of the RFC.

-->

      <reference anchor="BCP195"
                 target="http://www.rfc-editor.org/info/bcp195">
        <front>
          <title>Recommendations for Secure Use of Transport Layer Security
          (TLS) and Datagram Transport Layer Security (DTLS)</title>

          <author fullname="Y. Sheffer" initials="Y." surname="Sheffer">
            <organization/>
          </author>

          <author fullname="R. Holz" initials="R." surname="Holz">
            <organization/>
          </author>

          <author fullname="P. Saint-Andre" initials="P."
                  surname="Saint-Andre">
            <organization/>
          </author>

          <date month="May" year="2015"/>

          <abstract>
            <t>Transport Layer Security (TLS) and Datagram Transport Layer
            Security (DTLS) are widely used to protect data exchanged over
            application protocols such as HTTP, SMTP, IMAP, POP, SIP, and
            XMPP. Over the last few years, several serious attacks on TLS have
            emerged, including attacks on its most commonly used cipher suites
            and their modes of operation. This document provides
            recommendations for improving the security of deployed services
            that use TLS and DTLS. The recommendations are applicable to the
            majority of use cases.</t>
          </abstract>
        </front>

        <seriesInfo name="BCP" value="195"/>

        <seriesInfo name="RFC" value="7525"/>

        <seriesInfo name="DOI" value="10.17487/RFC7525"/>

        <format octets="60283" type="ASCII"/>
      </reference>
    </references>

    <section anchor="PoP" title="Use with Proof-of-Possession Tokens">
      <t>With bearer tokens such as those defined by <xref
      target="RFC6750">OAuth 2.0 Bearer Token Usage</xref>, the protected
      resource will have in its possession the entire secret portion of the
      token for submission to the introspection service. However, for
      proof-of-possession style tokens, the protected resource will have only
      a token identifier used during the request, along with the cryptographic
      signature on the request. To validate the signature on the request, the
      protected resource could be able to submit the token identifier to the
      authorization server's introspection endpoint to obtain the necessary
      key information needed for that token. The details of this usage are
      outside the scope of this specification and will be defined in an
      extension to this specification in concert with the definition of
      proof-of-possession tokens.</t>
    </section>

    <section numbered="no" title="Acknowledgements">
      <t>Thanks to the OAuth Working Group and the User Managed Access Working
      Group for feedback and review of this document, and to the various
      implementors of both the client and server components of this
      specification. In particular, the author would like to thank Amanda
      Anganes, John Bradley, Thomas Broyer, Brian Campbell, George Fletcher,
      Paul Freemantle, Thomas Hardjono, Eve Maler, Josh Mandel, Steve Moore,
      Mike Schwartz, Prabath Siriwardena, Sarah Squire, and Hannes
      Tschofennig.</t>
    </section>
  </back>
</rfc>