DecodeJWS policy

This page applies to Apigee and Apigee hybrid.

View Apigee Edge documentation.

What

Decodes the JWS header without verifying the signature on the JWS, and writes each header to a flow variable. This policy is most useful when used in concert with the VerifyJWS policy, when the value of a header from within the JWS must be known before verifying the signature of the JWS.

A JWS can have an attached payload, as in the form:

header.payload.signature

Or, the JWS can omit the payload, called a detached payload, and be in the form:

header..signature

The DecodeJWS policy works with both forms because it only decodes the header portion of the JWS. The DecodeJWS policy also works regardless of the algorithm that was used to sign the JWS.

See JWS and JWT policies overview for a detailed introduction and an overview of the format of a JWS.

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 decode a JWT. While this video is specific to a JWT, many of the concepts are the same for JWS.

Sample: Decode a JWS

The policy shown below decodes a JWS found in the flow variable var.JWS. This variable must be present and contain a viable (decodable) JWS. The policy can obtain the JWS from any flow variable.

<DecodeJWS name="JWS-Decode-HS256">
    <DisplayName>JWS Verify HS256</DisplayName>
    <Source>var.JWS</Source>
</DecodeJWS>

For each header in the header portion of the JWS, the policy sets a flow variable named:

jws.policy-name.header.header-name

If the JWS has an attached payload, then it sets the jws.policy-name.header.payload flow variable to the payload. For a detached payload, payload is empty. See Flow variables for a complete list of the variables set by this policy.

Element reference for Decode JWS

The policy reference describes the elements and attributes of the Decode JWS policy.

Attributes that apply to the top-level element

<DecodeJWS 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 management 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 management 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

<Source>

<Source>JWS-variable</Source>

If present, specifies the flow variable in which the policy expects to find the JWS to decode.

Note: By default, the JWS is retrieved from the variable request.header.authorization. In this case, Apigee looks for the JWS in the request Authorization header. If you pass the JWS in the Authorization header, you do not need to include the Source element in the policy; however, you must include Bearer in the auth header. For example, you would pass the JWS in the Authorization header like this:

curl -v http://52.200.92.187:9001/doctest-JWS/verify-rs256 -H "Authorization: Bearer <your JWS>"

You can configure to policy to retrieve the JWS from a form or query parameter variable or any other variable. If the variable does not exist or if the policy otherwise can't find the JWS, the policy returns an error.

Default	request.header.authorization (See the note above for important information about the default).
Presence	Optional
Type	String
Valid values	An Apigee flow variable name

Flow variables

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

jws.{policy_name}.{variable_name}

For example, if the policy name is verify-jws, then the policy will store the algorithm specified in the JWS to this context variable: jws.verify-jws.header.algorithm

Variable name	Description
decoded.header.name	The JSON-parsable value of a header in the payload. One variable is set for every header in the payload. While you can also use the header.name flow variables, this is the recommended variable to use to access a header.
header.algorithm	The signing algorithm used on the JWS. For example, RS256, HS384, and so on. See (Algorithm) Header Parameter for more.
header.kid	The Key ID, if added when the JWS was generated. See also "Using a JSON Web Key Set (JWKS)" at JWT and JWS policies overview to verify a JWS. See (Key ID) Header Parameter for more.
header.type	The header type value. See (Type) Header Parameter for more.
header.name	The value of the named header (standard or additional). One of these will be set for every additional header in the header portion of the JWS.
header-json	The header in JSON format.
payload	The JWS payload if the JWS has an attached payload. For a detached paylod, this variable is empty.
valid	In the case of VerifyJWS, this variable will be true when the signature is verified, and the current time is before the token expiry, and after the token notBefore value, if they are present. Otherwise false. In the case of DecodeJWS, this variable is not set.

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.FailedToDecode	401	The policy was unable to decode the JWS. The JWS is possibly corrupted.
steps.jws.FailedToResolveVariable	401	Occurs when the flow variable specified in the <Source> element of the policy does not exist.
steps.jws.InvalidClaim	401	For a missing claim or claim mismatch, or a missing header or header mismatch.
steps.jws.InvalidJsonFormat	401	Invalid JSON found in the JWS header.
steps.jws.InvalidJws	401	This error occurs when the JWS signature verification fails.
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.MissingPayload	401	The JWS payload is missing.
steps.jws.NoAlgorithmFoundInHeader	401	Occurs when the JWS omits the algorithm header.
steps.jws.UnknownException	401	An unknown exception occurred.

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>