GenerateJWS policy

This page applies to Apigee and Apigee hybrid.

View Apigee Edge documentation.

What

Generates a signed JWS, with a configurable set of claims. The JWS can then be returned to clients, transmitted to backend targets, or used in other ways. See JWS and JWT policies overview for a detailed introduction.

To learn about the parts of a JWS and how they are encrypted and signed, refer to RFC7515.

This policy is an Extensible policy and use of this policy might have cost or utilization implications, depending on your Apigee license. For information on policy types and usage implications, see Policy types.

Video

Note: The following video shows the classic Proxy Editor in the Apigee UI. Apigee is introducing a new version of the Proxy Editor, which has a different design from the classic version shown in the video.

Watch a short video to learn how to generate a signed JWT. While this video is specific to generating a JWT, many of the concepts are the same for JWS.

Samples

Generate a JWS signed with HS256

This example policy generates a JWS that is signed using the HS256 algorithm. HS256 relies on a shared secret for both signing and verifying the signature. This JWS uses "attached" content, meaning the encoded header, payload, and signature are dot-concatenated to produce the final JWS:

[header].[payload].[signature]

Use the <Payload> element to specify the raw, unencoded JWS payload. In this example, a variable contains the payload. When this policy action is triggered, Apigee encodes the JWS header and payload, then adds the encoded signature to digitally sign the JWS.

The policy configuration below creates a JWS from a payload contained in the variable my-payload, and stores the resulting JWS in the variable output-variable.

<GenerateJWS name="JWS-Generate-HS256">
    <DisplayName>JWS Generate HS256</DisplayName>
    <Algorithm>HS256</Algorithm>
    <IgnoreUnresolvedVariables>false</IgnoreUnresolvedVariables>
    <SecretKey>
        <Value ref="private.secretkey"/>
        <Id>1918290</Id>
    </SecretKey>
    <Payload ref="my-payload"/>
    <OutputVariable>output-variable</OutputVariable>
</GenerateJWS>

Generate an HS256-signed JWT

This example also generates a JWS with attached content that is signed using the HS256 algorithm. In this case, the payload is JSON. Setting the typ header to JWT results in a signed JWS that is also a signed JWT. (reference)

The policy configuration below creates a JWS from a payload contained in the variable json-content, and stores the resulting JWS in the variable output-variable. The result will be a signed JWT if and only if the json-content variable holds a JSON payload, and the properties within that JSON payload are valid for JWT. For example, the exp property, if it is present, must hold a numeric value. The aud property, if it is present, must be a string or an array of strings. And so on. Consult IETF RFC7519 for details on the valid values for JWT claims.

<GenerateJWS name="JWS-Generate-HS256-JWT">
    <Algorithm>HS256</Algorithm>
    <IgnoreUnresolvedVariables>false</IgnoreUnresolvedVariables>
    <SecretKey>
        <Value ref="private.secretkey"/>
    </SecretKey>
    <Payload ref="json-content"/>
    <AdditionalHeaders>
        <Claim name="typ">JWT</Claim>
    </AdditionalHeaders>
    <OutputVariable>output-variable</OutputVariable>
</GenerateJWS>

Generate a detached JWS

This example policy generates a JWS with detached content, signed using the RS256 algorithm. Generating an RS256 signature relies on an RSA private key, which must be provided in PEM-encoded form.

A JWS with detached content omits the payload from the generated JWS:

[header]..[signature]

See Parts of a JWS/JWT for more on the structure and format of a JWS.

Use the <Payload> element to specify the raw, unencoded JWS payload. When this policy is triggered, Apigee encodes the JWS header and payload, and then uses them to generate the encoded signature. However, the generated JWS omits the encoded payload from the serialized JWS. This is helpful when the signed content is large, or binary (such as an image or PDF), or both. To allow validation, you must pass both elements, the JWS and the payload that was included in the signed content, to the verifying party. If you are using the VerifyJWS policy to verify the JWS, you can specify the variable containing the payload with the <DetachedContent> element of the VerifyJWS policy.

<GenerateJWS name="JWS-Generate-RS256">
    <DisplayName>JWS Generate RS256</DisplayName>
    <Algorithm>RS256</Algorithm>
    <IgnoreUnresolvedVariables>false</IgnoreUnresolvedVariables>
    <PrivateKey>
        <Value ref="private.privatekey"/>
        <Password ref="private.privatekey-password"/>
        <Id ref="private.privatekey-id"/>
    </PrivateKey>
    <Payload ref="my-payload"/>
    <DetachContent>true</DetachContent>
    <OutputVariable>output-variable</OutputVariable>
</GenerateJWS>

Note: You can use a slightly modified version of this example to generate a JWS for the PS* or ES* algorithms. Just change the value of <Algorithm>RS256</Algorithm> to PS256, or ES256, etc. The key you specify must be compatible with the algorithm. For more on the key requirements, see About signature encryption algorithms.

Setting the key elements

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

Note: The RS*, PS*, and ES* algorithms all use the same elements to specify the key. The key data you provide must be compatible with the algorithm you specify. For more on the key requirements, see About signature encryption algorithms.

Algorithm	Key elements
HS{256/384/512}^*	<SecretKey> <Value ref="private.secretkey"/> <Id>1918290</Id> </SecretKey>
RS/PS/ES{256/384/512}^*	<PrivateKey> <Value ref="private.privatekey"/> <Password ref="private.privatekey-password"/> <Id ref="private.privatekey-id"/> </PrivateKey> The <Password> and <Id> elements are optional.
^*For more on the key requirements, see About signature encryption algorithms.

Element reference for Generate JWS

The policy reference describes the elements and attributes of the Generate JWS 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

<GenerateJWS name="JWS" continueOnError="false" enabled="true" async="false">

The following attributes are common to all policy parent elements.

Attribute	Description	Default	Presence
name	The internal name of the policy. Characters you can use in the name are restricted to: A-Z0-9._\-$ %. However, the Apigee UI enforces additional restrictions, such as automatically removing characters that are not alphanumeric. Optionally, use the <displayname></displayname> element to label the policy in the Apigee UI proxy editor with a different, natural-language name.	N/A	Required
continueOnError	Set to false to return an error when a policy fails. This is expected behavior for most policies. Set to true to have flow execution continue even after a policy fails.	false	Optional
enabled	Set to true to enforce the policy. Set to false to "turn off" the policy. The policy will not be enforced even if it remains attached to a flow.	true	Optional
async	This attribute is deprecated.	false	Deprecated

<DisplayName>

<DisplayName>Policy Display Name</DisplayName>

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

Default	If you omit this element, the value of the policy's name attribute is used.
Presence	Optional
Type	String

<Algorithm>

<Algorithm>algorithm-here</Algorithm>

Specifies the encryption algorithm to sign the token.

Default	N/A
Presence	Required
Type	String
Valid values	HS256, HS384, HS512, RS256, RS384, RS512, ES256, ES384, ES512, PS256, PS384, PS512

<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>

Puts the additional claim name/value pair(s) in the header for the JWS.

The <Claim> element supports the dynamic string substitution feature called message templating when type=map.

Default	N/A
Presence	Optional
Valid values	Any value that you want to use for an additional claim. You can specify the claim explicitly as string, a number, a boolean, a map, or an array.

The <Claim> element takes these attributes:

• name - (Required) The name of the claim, also known as the parameter.
• 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.

<CriticalHeaders>

<CriticalHeaders>a,b,c</CriticalHeaders>

or:

<CriticalHeaders ref="variable_containing_headers"/>

Adds the critical header, crit, to the JWS. The crit header is an array of header names that must be known and recognized by the JWS receiver. For example, you can use this configuration element to produce a JWS header that when decoded, looks like this:

{
  "typ": "...",
  "alg" : "...",
  "hyb" : "some-value-here",
  "crit" : [ "hyb" ],
}

This JWS header asserts that the hyb header parameter is of critical importance, and any recipient of the JWS must understand the meaning and value of that parameter.

Per IETF RFC 7515, the recipient of a JWS should reject the JWS as invalid if the recipient does not understand one or more of the parameters referenced in the crit parameter. In Apigee, the VerifyJWS policy conforms to this behavior. For each parameter listed in the crit parameter, it checks that the <KnownHeaders> element of the VerifyJWS policy also lists that parameter. Any header that the VerifyJWS policy finds in crit that is not also listed in <KnownHeaders> causes the VerifyJWS policy to reject the JWS.

Note: It is nonsensical to include in the list of CriticalHeaders any header parameters that do not exist in the actual JWS header. The <CriticalHeaders> does not actually add the referenced parameters to the JWS header. It only defines the contents of the crit parameter. You can use the <AdditionalHeader/Claims> to add the referenced header claims or parameters.

Default	N/A
Presence	Optional
Type	Comma separated array of one or more strings
Valid values	Either an array or a reference to a variable containing the array.

<DetachContent>

<DetachContent>true|false</DetachContent>

Specifies whether to generate the JWS with a detached payload, <DetachContent>true</DetachContent>, or not, <DetachContent>false</DetachContent>.

If you specify false, the default, the generated JWS is in the form:

[header].[payload].[signature]

If you specify true to create a JWS with a detached payload, the generated JWS omits the payload and is in the form:

[header]..[signature]

With a JWS using a detached payload, it is up to you to pass the original unencoded payload to the verifying party, along with the serialized JWS.

Default	false
Presence	Optional
Type	Boolean
Valid values	true or false

<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).

Default	false
Presence	Optional
Type	Boolean
Valid values	true or false

<OutputVariable>

<OutputVariable>output-variable</OutputVariable>

Specifies the name of the context variable that the policy will set with the generated JWS. By default, the policy places the JWS into the context variable named jws.POLICYNAME.generated_jws.

Default	jws.POLICYNAME.generated_jws
Presence	Optional
Type	String (a flow variable name)

<Payload>

<Payload ref="flow-variable-name-here" />

or

<Payload>payload-value</Payload>

Specifies the raw, unencoded JWS payload. Specify a variable containing the payload, or a string.

The <Payload> element supports the dynamic string substitution feature called message templating. A message template permits you to perform variable string substitution in the payload-value string. In the following example, the payload would be constructed from a combination of text and the value of a variable.

<Payload>fixed-text-{request.formparam.payload}-more-fixed-text</Payload>

Default	N/A
Presence	Required
Type	String, byte array, stream, or any other representation of the unencoded JWS payload.
Valid values	Either a message template, or a reference to a variable containing the payload.

<PrivateKey> element

This is optional, for use only when the <Algorithm> is one of the RS*, PS*, or ES* options. It specifies the private key to use for signing, as well as other information related to the private key. It is used when the algorithm is an asymmetric algorithm.

<PrivateKey>
   <Value ref="private.privatekey"</Value>
</PrivateKey>

Default:	N/A
Presence:	Optional. However, you must include exactly one of either the <PrivateKey> or <SecretKey> element. Use the <PrivateKey> element when the algorithm is RS*, PS*, or ES*, and use the <SecretKey> element when the algorithm is HS*.
Type:	N/A

<PrivateKey/Id>

<PrivateKey>
  <Id ref="flow-variable-name-here"/>
</PrivateKey>

or

<PrivateKey>
  <Id>your-id-value-here</Id>
</PrivateKey>

Specifies the key ID (kid) to include in the JWS header.

Default	N/A
Presence	Optional
Type	String
Valid values	A flow variable or string

<PrivateKey/Password>

<PrivateKey>
  <Password ref="private.privatekey-password"/>
</PrivateKey>

Specify the password the policy should use to decrypt the private key, if necessary. Use the ref attribute to pass the key in a flow variable.

Default	N/A
Presence	Optional
Type	String
Valid values	A flow variable reference. Note: You must specify a flow variable with the ref attribute. Apigee will reject as invalid a policy configuration in which the password is specified in plaintext. The flow variable must have the prefix "private". For example, private.mypassword

<PrivateKey/Value>

<PrivateKey>
  <Value ref="private.variable-name-here"/>
</PrivateKey>

Specifies a PEM-encoded private key used to sign the JWS. Use the ref attribute to pass the key in a flow variable.

Default	N/A
Presence	Required when using the policy to generate a JWS using one of the RS*, PS*, or ES* algorithms.
Type	String
Valid values	A flow variable containing a string representing a PEM-encoded private key value. Note: The flow variable must have the prefix "private". For example, private.mykey

<SecretKey>

<SecretKey encoding="base16|hex|base64|base64url" >
  <Id ref="variable-containing-key-id-here">secret-key-id</Id>
  <Value ref="private.variable-here"/>
</SecretKey>

Specifies the secret key to use when generating a JWS that uses a symmetric (HS*) algorithm, one of HS256, HS384, or HS512.

This element is optional. However, you must include exactly one of either the <PrivateKey> or <SecretKey> element. Use the <PrivateKey> element when generating a JWS signed with an asymmetric algorithm (one of RS*, PS*, or ES*), and use the <SecretKey> element when generating a JWS signed with a symmetric algorithm (algorithm like HS*).

Children of <SecretKey>

The following table provides a description of the child elements and attributes of <SecretKey>:

Child	Presence	Description
encoding (attribute)	Optional	Specifies how the key is encoded in the referenced variable. By default, when no encoding attribute is present, the encoding of the key is treated as UTF-8. Valid values for the attribute are: hex, base16, base64, or base64url. The encoding values hex and base16 are synonyms. <SecretKey encoding="hex" > <Id ref="variable-containing-key-id-here">secret-key-id</Id> <Value ref="private.secretkey"/> </SecretKey> In the above example, because the encoding is hex, if the contents of the variable private.secretkey is 494c6f766541504973, the key will be decoded as a set of 9 bytes, which in hex will be 49 4c 6f 76 65 41 50 49 73. Note: Apigee enforces a minimum key strength. See the documentation for the Value element for details.
Id (element)	Optional	The key identifier. The value can be any string. You can specify the value as a literal text value, or indirectly, via a variable reference, with the ref attribute. <SecretKey> <Id ref="flow-variable-name-here"/> <Value ref="private.variable-here"/> </SecretKey> or <SecretKey> <Id>your-id-value-here</Id> <Value ref="private.variable-here"/> </SecretKey> The policy will include this key identifier as the kid claim in the header of the generated JWS.
Value (element)	Required	An encoded secret key. Specifies the secret key used to sign the payload. Use the ref attribute to provide the key indirectly via a variable, such as private.secret-key . <SecretKey> <Id ref="flow-variable-name-here"/> <Value ref="private.my-secret-variable"/> </SecretKey> Note: The variable name must include the private prefix as shown in the example above. Apigee enforces a minimum key strength for the HS256/HS384/HS512 algorithms. The minimum key length for HS256 is 32 bytes, for HS384 it is 48 bytes, and for HS512 it is 64 bytes. Using a lower-strength key causes a runtime error.

<Type>

<Type>type-string-here</Type>

Optional element whose only allowed value is Signed, specifying that the policy generates a signed JWS. <Type> is provided just to match the corresponding element for the GenerateJWT and VerifyJWT policies (where it can take on either of the values Signed or Encrypted).

Default	N/A
Presence	Optional
Type	String
Valid value	Signed

Flow variables

The Generate JWS policy does not set flow variables.

Error reference

This section describes the fault codes and error messages that are returned and fault variables that are set by Apigee 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.

Fault code	HTTP status	Occurs when
steps.jws.GenerationFailed	401	The policy was unable to generate the JWS.
steps.jws.InsufficientKeyLength	401	For a key less than 32 bytes for the HS256 algorithm
steps.jws.InvalidClaim	401	For a missing claim or claim mismatch, or a missing header or header mismatch.
steps.jws.InvalidCurve	401	The curve specified by the key is not valid for the Elliptic Curve algorithm.
steps.jws.InvalidJsonFormat	401	Invalid JSON found in the JWS header.
steps.jws.InvalidPayload	401	The JWS payload is invalid.
steps.jws.InvalidSignature	401	<DetachedContent> is omitted and the JWS has a detached content payload.
steps.jws.KeyIdMissing	401	The Verify policy uses a JWKS as a source for public keys, but the signed JWS does not include a kid property in the header.
steps.jws.KeyParsingFailed	401	The public key could not be parsed from the given key information.
steps.jws.MissingPayload	401	The JWS payload is missing.
steps.jws.NoAlgorithmFoundInHeader	401	Occurs when the JWS omits the algorithm header.
steps.jws.SigningFailed	401	In GenerateJWS, for a key less than the minimum size for the HS384 or HS512 algorithms
steps.jws.UnknownException	401	An unknown exception occurred.
steps.jws.WrongKeyType	401	Wrong type of key specified. For example, if you specify an RSA key for an Elliptic Curve algorithm, or a curve key for an RSA algorithm.

Deployment errors

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

Error name	Occurs when
InvalidAlgorithm	The only valid values are: RS256, RS384, RS512, PS256, PS384, PS512, ES256, ES384, ES512, HS256, HS384, HS512.
EmptyElementForKeyConfiguration FailedToResolveVariable InvalidConfigurationForActionAndAlgorithmFamily InvalidConfigurationForVerify InvalidEmptyElement InvalidFamiliesForAlgorithm InvalidKeyConfiguration InvalidNameForAdditionalClaim InvalidNameForAdditionalHeader InvalidPublicKeyId InvalidPublicKeyValue InvalidSecretInConfig InvalidTypeForAdditionalClaim InvalidTypeForAdditionalHeader InvalidValueForElement InvalidValueOfArrayAttribute InvalidVariableNameForSecret MissingConfigurationElement MissingElementForKeyConfiguration MissingNameForAdditionalClaim MissingNameForAdditionalHeader	Other possible deployment errors.

Fault variables

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

Variables	Where	Example
fault.name="fault_name"	fault_name is the name of the fault, as listed in the Runtime errors table above. The fault name is the last part of the fault code.	fault.name Matches "TokenExpired"
JWS.failed	All JWS policies set the same variable in the case of a failure.	jws.JWS-Policy.failed = true

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