VerifyJWT policy

You're viewing Apigee Edge documentation.
Go to the Apigee X documentation. info

What

Verifies the signature on a JWT received from clients or other systems. This policy also extracts the claims into context variables so that subsequent policies or conditions can examine those values to make authorization or routing decisions. See JWS and JWT policies overview for a detailed introduction.

When this policy executes, Edge verifies the signature of a JWT, and verifies that the JWT is valid according to the expiry and not-before times if they are present. The policy can optionally also verify the values of specific claims on the JWT, such as the subject, the issuer, the audience, or the value of additional claims.

If the JWT is verified and valid, then all of the claims contained within the JWT are extracted into context variables for use by subsequent policies or conditions, and the request is allowed to proceed. If the JWT signature cannot be verified or if the JWT is invalid because of one of the timestamps, all processing stops and an error is returned in the response.

To learn about the parts of a JWT and how they are encrypted and signed, refer to RFC7519.

Video

Watch a short video to learn how to verify the signature on a JWT.

Samples

• Verify a JWT signed with the HS256 algorithm
• Verify a JWT signed with the RS256 algorithm

Verify a JWT signed with the HS256 algorithm

This example policy verifies a JWT that was signed with the HS256 encryption algorithm, HMAC using a SHA-256 checksum. The JWT is passed in the proxy request by using a form parameter named jwt. The key is contained in a variable named private.secretkey. See the video above for a complete example, including how to make a request to the policy.

The policy configuration includes the information Edge needs to decode and evaluate the JWT, such as where to find the JWT (in a flow variable specified in the Source element), the required signing algorithm, where to find the secret key (stored in an Edge flow variable, which could have been retrieved from the Edge KVM, for example), and a set of required claims and their values.

<VerifyJWT name="JWT-Verify-HS256">
    <DisplayName>JWT Verify HS256</DisplayName>
    <Algorithm>HS256</Algorithm>
    <Source>request.formparam.jwt</Source>
    <IgnoreUnresolvedVariables>false</IgnoreUnresolvedVariables>
    <SecretKey encoding="base64">
        <Value ref="private.secretkey"/>
    </SecretKey>
    <Subject>monty-pythons-flying-circus</Subject>
    <Issuer>urn://apigee-edge-JWT-policy-test</Issuer>
    <Audience>fans</Audience>
    <AdditionalClaims>
        <Claim name="show">And now for something completely different.</Claim>
    </AdditionalClaims>
</VerifyJWT>

The policy writes its output to context variables so that subsequent policies or conditions in the API proxy can examine those values. See Flow variables for a list of the variables set by this policy.

Verify a JWT signed with the RS256 algorithm

This example policy verifies a JWT that was signed with the RS256 algorithm. To verify, you need to provide the public key. The JWT is passed in the proxy request by using a form parameter named jwt. The public key is contained in a variable named public.publickey. See the video above for a complete example, including how to make a request to the policy.

See the Element reference for details on the requirements and options for each element in this sample policy.

<VerifyJWT name="JWT-Verify-RS256">
    <Algorithm>RS256</Algorithm>
    <Source>request.formparam.jwt</Source>
    <IgnoreUnresolvedVariables>false</IgnoreUnresolvedVariables>
    <PublicKey>
        <Value ref="public.publickey"/>
    </PublicKey>
    <Subject>apigee-seattle-hatrack-montage</Subject>
    <Issuer>urn://apigee-edge-JWT-policy-test</Issuer>
    <Audience>urn://c60511c0-12a2-473c-80fd-42528eb65a6a</Audience>
    <AdditionalClaims>
        <Claim name="show">And now for something completely different.</Claim>    
    </AdditionalClaims>
</VerifyJWT>

For the above configuration, a JWT with this header …

{
  "typ" : "JWT", 
  "alg" : "RS256"
}

And this payload …

{ 
  "sub" : "apigee-seattle-hatrack-montage",
  "iss" : "urn://apigee-edge-JWT-policy-test",
  "aud" : "urn://c60511c0-12a2-473c-80fd-42528eb65a6a",
  "show": "And now for something completely different."
}

… will be deemed as valid, if the signature can be verified with the provided public key.

A JWT with the same header but with this payload …

{ 
  "sub" : "monty-pythons-flying-circus",
  "iss" : "urn://apigee-edge-JWT-policy-test",
  "aud" : "urn://c60511c0-12a2-473c-80fd-42528eb65a6a",
  "show": "And now for something completely different."
}

… will be determined to be invalid, even if the signature can be verified, because the "sub" claim included in the JWT does not match the required value of the "Subject" element as specified in the policy configuration.

The policy writes its output to context variables so that subsequent policies or conditions in the API proxy can examine those values. See Flow variables for a list of the variables set by this policy.

Setting the key elements

The elements that you use to specify the key used to verify the JWT depend on the chosen algorithm, as shown in the following table:

<SecretKey encoding="base16|hex|base64|base64url">
  <Value ref="private.secretkey"/>
</SecretKey>

<PublicKey>
  <Value ref="rsa_public_key_or_value"/>
</PublicKey>

<PublicKey>
  <Certificate ref="signed_cert_val_ref"/>
</PublicKey>

<PublicKey>
  <JWKS ref="jwks_val_or_ref"/>
</PublicKey>

Element reference

The policy reference describes the elements and attributes of the Verify JWT policy.

Note: Configuration will differ somewhat depending on the encryption algorithm you use. Refer to the Samples for examples that demonstrate configurations for specific use cases.

Attributes that apply to the top-level element

<VerifyJWT name="JWT" continueOnError="false" enabled="true" async="false">

The following attributes are common to all policy parent elements.

<DisplayName>

<DisplayName>Policy Display Name</DisplayName>

Use in addition to the name attribute to label the policy in the management UI proxy editor with a different, natural-language name.

<Algorithm>

<Algorithm>HS256</Algorithm>

Specifies the encryption algorithm to sign the token. RS*/PS*/ES* algorithms employ a public/secret key pair, while HS* algorithms employ a shared secret. See also About signature encryption algorithms.

You can specify multiple values separated by commas. For example "HS256, HS512" or "RS256, PS256". However, you cannot combine HS* algorithms with any others or ES* algorithms with any others because they require a specific key type. You can combine RS* and PS* algorithms.

<Audience>

<Audience>audience-here</Audience>

or:

<Audience ref='variable-name-here'/>

The policy verifies that the audience claim in the JWT matches the value specified in the configuration. If there is no match, the policy throws an error. This claim identifies the recipients that the JWT is intended for. This is one of the registered claims mentioned in RFC7519.

<AdditionalClaims/Claim>

<AdditionalClaims>
    <Claim name='claim1'>explicit-value-of-claim-here</Claim>
    <Claim name='claim2' ref='variable-name-here'/>
    <Claim name='claim3' ref='variable-name-here' type='boolean'/>
 </AdditionalClaims>

or:

<AdditionalClaims ref='claim_payload'/>

Validates that the JWT payload contains the specified additional claim(s) and that the asserted claim values match.

An additional claim uses a name that is not one of the standard, registered JWT claim names. The value of a additional claim can be a string, a number, a boolean, a map, or an array. A map is simply a set of name/value pairs. The value for a claim of any of these types can be specified explicitly in the policy configuration, or indirectly via a reference to a flow variable.

The <Claim> element takes these attributes:

• name - (Required) The name of the claim.
• ref - (Optional) The name of a flow variable. If present, the policy will use the value of this variable as the claim. If both a ref attribute and an explicit claim value are specified, the explicit value is the default, and is used if the referenced flow variable is unresolved.
• type - (Optional) One of: string (default), number, boolean, or map
• array - (Optional) Set to true to indicate if the value is an array of types. Default: false.

When you include the <Claim> element, the claim names are set statically when you configure the policy. Alternatively, you can pass a JSON object to specify the claim names. Because the JSON object is passed as a variable, the claim names are determined at runtime.

For example:

<AdditionalClaims ref='json_claims'/>

Where the variable json_claims contains a JSON object in the form:

{
  "sub" : "person@example.com",
  "iss" : "urn://secure-issuer@example.com",
  "non-registered-claim" : {
    "This-is-a-thing" : 817,
    "https://example.com/foobar" : { "p": 42, "q": false }
  }
}

<AdditionalHeaders/Claim>

<AdditionalHeaders>
    <Claim name='claim1'>explicit-value-of-claim-here</Claim>
    <Claim name='claim2' ref='variable-name-here'/>
    <Claim name='claim3' ref='variable-name-here' type='boolean'/>
    <Claim name='claim4' ref='variable-name' type='string' array='true'/>
 </AdditionalHeaders>

Validates that the JWT header contains the specified additional claim name/value pair(s) and that the asserted claim values match.

An additionl claim uses a name that is not one of the standard, registered JWT claim names. The value of an additional claim can be a string, a number, a boolean, a map, or an array. A map is simply a set of name/value pairs. The value for a claim of any of these types can be specified explicitly in the policy configuration, or indirectly via a reference to a flow variable.

The <Claim> element takes these attributes:

• name - (Required) The name of the claim.
• ref - (Optional) The name of a flow variable. If present, the policy will use the value of this variable as the claim. If both a ref attribute and an explicit claim value are specified, the explicit value is the default, and is used if the referenced flow variable is unresolved.
• type - (Optional) One of: string (default), number, boolean, or map
• array - (Optional) Set to true to indicate if the value is an array of types. Default: false.

<CustomClaims>

Note: Currently, a CustomClaims element is inserted when you add a new GenerateJWT policy through the UI. This element is not functional and is ignored. The correct element to use instead is <AdditionalClaims>. The UI will be updated to insert the correct elements at a later time.

<Id>

<Id>explicit-jti-value-here</Id>
 -or-
<Id ref='variable-name-here'/>
 -or-
<Id/>

Verifies that the JWT has the specific jti claim. When the text value and ref attribute are both empty, the policy will generate a jti containing a random UUID. The JWT ID (jti) claim is a unique identifier for the JWT. For more information on jti, refer to RFC7519.

<IgnoreCriticalHeaders>

<IgnoreCriticalHeaders>true|false</IgnoreCriticalHeaders>

Set to false if you want the policy to throw an error when any header listed in the crit header of the JWT is not listed in the <KnownHeaders> element. Set to true to cause the VerifyJWT policy to ignore the crit header.

One reason to set this element to true is if you are in a testing environment and are not yet ready to casues a failure on a missing header.

<IgnoreIssuedAt>

<IgnoreIssuedAt>true|false</IgnoreIssuedAt>

Set to false (default) if you want the policy to throw an error when a JWT contains an iat (Issued at) claim that specifies a time in the future. Set to true to cause the policy to ignore iat during verification.

<IgnoreUnresolvedVariables>

<IgnoreUnresolvedVariables>true|false</IgnoreUnresolvedVariables>

Set to false if you want the policy to throw an error when any referenced variable specified in the policy is unresolvable. Set to true to treat any unresolvable variable as an empty string (null).

<Issuer>

<Issuer ref='variable-name-here'/>
<Issuer>issuer-string-here</Issuer>

The policy verifies that the issuer in the JWT matches the string specified in the configuration element. A claim that identifies the issuer of the JWT. This is one of the registered set of claims mentioned in RFC7519.

<KnownHeaders>

<KnownHeaders>a,b,c</KnownHeaders>

or:

<KnownHeaders ref=’variable_containing_headers’/>

The GenerateJWT policy uses the <CriticalHeaders> element to populate the crit header in a JWT. For example:

{
  “typ: “...”,
  “alg” : “...”,
  “crit” : [ “a”, “b”, “c” ],
}

The VerifyJWT policy examines crit header in the JWT, if it exists, and for each header listed it checks that the <KnownHeaders> element also lists that header. The <KnownHeaders> element can contain a superset of the items listed in crit. It is only necessary that all the headers listed in crit are listed in the <KnownHeaders> element. Any header that the policy finds in crit that is not also listed in <KnownHeaders> causes the VerifyJWT policy to fail.

You can optionally configure the VerifyJWT policy to ignore the crit header by setting the <IgnoreCriticalHeaders> element to true.

<PublicKey/Certificate>

<PublicKey>
   <Certificate ref="signed_public.cert"/>
</PublicKey>
-or-
<PublicKey>
    <Certificate>
    -----BEGIN CERTIFICATE-----
    cert data
    -----END CERTIFICATE-----
    </Certificate>
</PublicKey>

Specifies the signed certificate used to verify the signature on the JWT. Use the ref attribute to pass the signed certificate in a flow variable, or specify the PEM-encoded certificate directly. Use only when the algorithm is one of RS256/RS384/RS512, PS256/PS384/PS512, or ES256/ES384/ES512.

<PublicKey/JWKS>

<!-- Specify the JWKS. -->
<PublicKey>
   <JWKS>jwks-value-here</JWKS>
</PublicKey>

or:

<!-- Specify a variable containing the JWKS. -->
<PublicKey>
   <JWKS ref="public.jwks"/>
</PublicKey>

or:

<!-- Specify a public URL that returns the JWKS.
The URL is static, meaning you cannot set it using a variable. -->
<PublicKey>
   <JWKS uri="jwks-url"/>
</PublicKey>

Specifies a value in JWKS format (RFC 7517) containing a set of public keys. Use only when the algorithm is one of RS256/RS384/RS512, PS256/PS384/PS512, or ES256/ES384/ES512.

If the inbound JWT bears a key ID which present in the set of JWKS, then the policy will use the correct public key to verify the JWT signature. For details about this feature, see Using a JSON Web Key Set (JWKS) to verify a JWT.

If you fetch the value from a public URL, Edge caches the JWKS for a period of 300 seconds. When the cache expires, Edge fetches the JWKS again.

<PublicKey/Value>

<PublicKey>
   <Value ref="public.publickeyorcert"/>
</PublicKey>
-or-
<PublicKey>
    <Value>
    -----BEGIN PUBLIC KEY-----
    MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAw2kPrRzcufvUNHvTH/WW
    Q0UrCw5c0+Y707KX3PpXkZGbtTT4nvU1jC0d1lHV8MfUyRXmpmnNxJHAC2F73IyN
    C5TBtXMORc+us7A2cTtC4gZV256bT4h3sIEMsDl0Joz9K9MPzVPFxa1i0RgNt06n
    Xn/Bs2UbbLlKP5Q1HPxewUDEh0gVMqz9wdIGwH1pPxKvd3NltYGfPsUQovlof3l2
    ALvO7i5Yrm96kknfFEWf1EjmCCKvz2vjVbBb6mp1ZpYfc9MOTZVpQcXSbzb/BWUo
    ZmkDb/DRW5onclGzxQITBFP3S6JXd4LNESJcTp705ec1cQ9Wp2Kl+nKrKyv1E5Xx
    DQIDAQAB
    -----END PUBLIC KEY-----
    </Value>
</PublicKey>

Specifies the public key or public cert used to verify the signature on the JWT. Use the ref attribute to pass the key/cert in a flow variable, or specify the PEM-encoded key directly. Use only when the algorithm is one of RS256/RS384/RS512, PS256/PS384/PS512, or ES256/ES384/ES512.

<SecretKey/Value>

<SecretKey encoding="base16|hex|base64|base64url">
  <Value ref="private.your-variable-name"/>
</SecretKey>

Provides the secret key used to verify or sign tokens with an HMAC algorithm. Use only when the algorithm is one of HS256, HS384, HS512..

<Source>

<Source>jwt-variable</Source>

If present, specifies the flow variable in which the policy expects to find the JWT to verify.

<Subject>

<Subject>subject-string-here</Subject>

The policy verifies that the subject in the JWT matches the string specified in the policy configuration. This claim identifies or makes a statement about the subject of the JWT. This is one of the standard set of claims mentioned in RFC7519.

<TimeAllowance>

<TimeAllowance>120s</TimeAllowance>

The "grace period" for times. For example, if the time allowance is configured to be 60s, then an expired JWT would be treated as still valid, for 60s after the asserted expiry. The not-before-time will be evaluated similarly. Defaults to 0 seconds (no grace period).

Flow variables

Upon success, the Verify JWT and Decode JWT policies set context variables according to this pattern:

jwt.{policy_name}.{variable_name}

For example, if the policy name is jwt-parse-token , then the policy will store the subject specified in the JWT to the context variable named jwt.jwt-parse-token.decoded.claim.sub. (For backward compatibility, it will also be available in jwt.jwt-parse-token.claim.subject)

Error reference

This section describes the fault codes and error messages that are returned and fault variables that are set by Edge when this policy triggers an error. This information is important to know if you are developing fault rules to handle faults. To learn more, see What you need to know about policy errors and Handling faults.

Runtime errors

These errors can occur when the policy executes.

Deployment errors

These errors can occur when you deploy a proxy containing this policy.

Fault variables

These variables are set when a runtime error occurs. For more information, see What you need to know about policy errors.

Example error response

For error handling, the best practice is to trap the errorcode part of the error response. Do not rely on the text in the faultstring, because it could change.

Example fault rule

    <FaultRules>
        <FaultRule name="JWT Policy Errors">
            <Step>
                <Name>JavaScript-1</Name>
                <Condition>(fault.name Matches "TokenExpired")</Condition>
            </Step>
            <Condition>JWT.failed=true</Condition>
        </FaultRule>
    </FaultRules>