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Passing Enduser Attributes to the Backend Using JWT

JSON Web Token (JWT) is used to represent claims that are transferred between two parties such as the end user and the backend.

A claim is an attribute of the user that is mapped to the underlying user store. It is encoded as a JavaScript Object Notation (JSON) object that is used as the payload of a JSON Web Signature (JWS) structure, or as the plain text of a JSON Web Encryption (JWE) structure. This enables claims to be digitally signed.

A set of claims is referred to as a dialect (e.g., http://wso2.org/claims). The general format of a JWT is {token infor}.{claims list}.{signature}. The API implementation uses information such as logging, content filtering and authentication/authorization that is stored in this token. The token is Base64-encoded and sent to the API implementation in a HTTP header variable. The JWT is self-contained and is divided into three parts as the header, the payload and the signature. For more information on JWT, see JSON Web Token (JWT) Overview.

The API Manager passes attributes of the API invoker to the backend API implementation using JWT to authenticate end users. In most production deployments, service calls go through WSO2 API Manager or a proxy service. If you enable JWT generation in WSO2 API Manager, each API request will carry a JWT to the back-end service. When the request goes through the API Manager, the JWT is appended as a transport header to the outgoing message. The back-end service fetches the JWT and retrieves the required information about the user, application, or token.

An example of a JWT is given below:

{
    "typ":"JWT",
    "alg":"NONE"
    }{
    "iss":"wso2.org/products/am",
    "exp":1345183492181,
    "http://wso2.org/claims/subscriber":"admin",
    "http://wso2.org/claims/applicationname":"app2",
    "http://wso2.org/claims/apicontext":"/placeFinder",
    "http://wso2.org/claims/version":"1.0.0",
    "http://wso2.org/claims/tier":"Silver",
    "http://wso2.org/claims/enduser":"sumedha"
    }

The above JWT access token contains the following information.

JWT Header : The header section declares that the encoded object is a JSON Web Token (JWT) and the JWT is in plain text, that is not signed using any encryption algorithm.

JWT Claims set :

• "iss" - The issuer of the JWT
• "exp" - The token expiration time
• "http://wso2.org/claims/subscriber" - Subscriber to the API, usually the app developer
• " http://wso2.org/claims/applicationname " - Application through which API invocation is done
• " http://wso2.org/claims/apicontext " - Context of the API
• " http://wso2.org/claims/version " - API version
• " http://wso2.org/claims/tier " - Tier/price band for the subscription
• " http://wso2.org/claims/enduser " - End-user of the app who's action invoked the API

Let's see how to enable and pass information in the JWT or completely alter the JWT generation logic in WSO2 API Manager:

Configuring JWT

Before passing end-user attributes, you need to enable and configure the JWT implementation in the <API-M_HOME>/repository/conf/deployment.toml file. The relevant elements are described below. If you do not configure these elements, they take their default values.

Note

Enable JWT in all Gateway and Key Manager nodes. For more information on setting up a distributed deployment of API Manager, see Deploying WSO2 API-M in a Distributed Setup.

Element	Description	Default Value
apim.jwt.enable	Uncomment this property and set this value to true to enable JWT.	false
apim.jwt.header	The name of the HTTP header to which the JWT is attached.	X-JWT-Assertion
apim.jwt.claims_extractor_impl	By default, the claims_extractor_impl parameter is commented out in the deployment.toml file. Enable it to add all user claims in the JWT access token: claims_extractor_impl = "org.wso2.carbon.apimgt.impl.token.DefaultClaimsRetriever" By default, the following are encoded to the JWT: subscriber name application name API context API version authorized resource owner name In addition, you can also write your own class by extending the interface org.wso2.carbon.apimgt.impl.token.ClaimsRetriever and implementing the following methods of the interface: Method Description void init() throws APIManagementException; Used to perform initialization tasks. Is executed once, right before the very first request. SortedMap<String,String> getClaims(String endUserName) throws APIManagementException; Returns a sorted map of claims. The key of the map indicates the user attribute name and the value indicates the corresponding user attribute value. The order in which these keys and values are encoded depends on the ordering defined in the sorted map. String getDialectURI(String endUserName); The dialect URI to which the attribute names returned by the getClaims() method are appended. For example, if the getClaims method returns {email:[email protected], gender:male} and the getDialectURI() returns http://wso2.org/claims, the JWT will contain "http://wso2.org/claims/gender":"male","http://wso2.org/claims/email":"[email protected]" as part of the body. The default implementation (org.wso2.carbon.apimgt.impl.token.DefaultClaimsRetriever) returns the user's attributes defined under the dialect URI http://wso2.org/claims and the JWT will also be encoded with the same dialect URI. The order of encoding the user's attributes is the natural order of the attributes. If no value is specified, no additional claims will be encoded, except the 6 default attributes.	org.wso2.carbon.apimgt.impl.token.DefaultClaimsRetriever
apim.jwt.claim_dialect	The dialect URI under which the user's claims are be looked for. Only works with the default value of the apim.jwt.claims_extractor_impl element defined above. The JWT access token contains all claims that are defined in the apim.jwt.claim_dialect element. The default value of this element is http://wso2.org/claims. To get the list of a specific user's claims that need to be included in the JWT, simply uncomment this element after enabling the JWT. It will include all claims in http://wso2.org/claims to the JWT access token.	http://wso2.org/claims
apim.jwt.signing_algorithm	The signing algorithm used to sign the JWT. The general format of the JWT is {token infor}.{claims list}.{signature}. When NONE is specified as the algorithm, signing is turned off and the JWT looks as {token infor}.{claims list} with two strings delimited by a period and a period at the end. This element can have only two values - the default values are `SHA256withRSA` or `NONE`.	SHA256withRSA

Tip

You can use TCPMon or API Gateway debug logs to capture the JWT access token header with end-user details. Follow the instructions below to enable the Gateway DEBUG logs for wire messages:

1. Go to the <APIM_GATEWAY>/repository/conf directory and open the log4j2.properties file with a text editor.
2. Add these two loggers to the list of loggers:
   loggers = AUDIT_LOG, trace-messages,... , synapse-headers, synapse-wire

Customizing the JWT generation

The JWT that is generated by default (see example above) has predefined attributes that are passed to the backend. These include basic application-specific details, subscription details, and user information that are defined in the JWT generation class that comes with WSO2 API Manager by the name org.wso2.carbon.apimgt.keymgt.token.JWTGenerator. 

Follow the instructions below if you want to pass additional attributes to the backend with the JWT or completely change the default JWT generation logic:

1. Write your own custom JWT implementation class by extending the default JWTGenerator class. A typical example of implementing your own claim generator is given below. It implements the populateCustomClaims() method to generate some custom claims and adds them to the JWT.

   import org.wso2.carbon.apimgt.keymgt.APIConstants;
   import org.wso2.carbon.apimgt.keymgt.dto.APIKeyValidationInfoDTO;
   import org.wso2.carbon.apimgt.keymgt.token.JWTGenerator;
   import org.wso2.carbon.apimgt.api.*;
   
   import java.util.Map;
   
   public class CustomTokenGenerator extends JWTGenerator {
       public Map<String, String> populateStandardClaims(TokenValidationContext validationContext)
               throws APIManagementException {
           Map<String, String> claims = super.populateStandardClaims(validationContext);
           boolean isApplicationToken =
                   validationContext.getValidationInfoDTO().getUserType().equalsIgnoreCase(APIConstants.ACCESS_TOKEN_USER_TYPE_APPLICATION) ? true : false;
           String dialect = getDialectURI();
           if (claims.get(dialect + "/enduser") != null) {
               if (isApplicationToken) {
                   claims.put(dialect + "/enduser", "null");
                   claims.put(dialect + "/enduserTenantId", "null");
               } else {
                   String enduser = claims.get(dialect + "/enduser");
                   if (enduser.endsWith("@carbon.super")) {
                       enduser = enduser.replace("@carbon.super", "");
                       claims.put(dialect + "/enduser", enduser);
                   }
               }
           }
           return claims;
       }
   
   
   
       public Map<String, String> populateCustomClaims(TokenValidationContext tokenValidationContext) throws APIManagementException {
           Long time = System.currentTimeMillis();
           String text = "This is custom JWT";
           Map map = new HashMap();
           map.put("current_timestamp", time.toString());
           map.put("messge" , text);
           return map;
       }
   }

   Click here for a sample Custom JWT Generator.

2. Build your class and add the JAR file to the <API-M_HOME>/repository/components/lib directory.

3. Add your class in the apim.jwt.generator_impl element of the <API-M_HOME>/repository/conf/deployment.toml file.

   [apim.jwt]
   ...
   generator_impl = "org.wso2.carbon.test.CustomTokenGenerator"

4. Set the apim.jwt.enable element to true in the deployment.toml file.

5. Restart the server.

Changing the JWT encoding to Base64URL encoding

The default JWT generator, org.wso2.carbon.apimgt.impl.token.JWTGenerator, encodes the value of the JWT using Base64 encoding. However, for certain apps you might need to have it in Base64URL encoding.

Use the following format to encode the JWT using Base64URL encoding, by adding the URLSafeJWTGenerator class in the apim.jwt.generator_impl element, which is in the <API-M_HOME>/repository/conf/deployment.toml file.

[apim.jwt]
...
generator_impl = "org.wso2.carbon.apimgt.keymgt.token.URLSafeJWTGenerator"

Expiry time of the JWT

JWT expiry time depends directly on whether caching is enabled in the Gateway Manager or Key Manager. The WSO2 API-M Gateway caching is enabled by default. However, if required, you can enable or disable the caching for the Gateway Manager or the Key Manager using the apim.cache.gateway_token.enable or apim.cache.km_token.enable elements respectively in the <API-M_HOME>/repository/conf/deployment.toml file. If caching is enabled for the Gateway Manager or the Key Manager, the JWT expiry time will be the same as the default cache expiry time.

The claims that are retrieved for the JWT access token generation are cached. The expiry time of these JWT claims can be set by setting the apim.cache.jwt_claim.expiry_time in the deployment.toml file:

[apim.cache.jwt_claim]
enable = true
expiry_time = "900"

Note

WSO2 API Manager comes with the default JWT generator. This JWT generator will generate specific claims according to the specifications and the user demands by the time we release the product. And when we update the products, we will need to add/change some of the claims according to the specification updates. That means even with the given released version, standard claims that come from the API Manager subjected to change. So if you have planned to use specific claims at the backend side it is always recommended to implement a custom JWT generator with mandatory claims you wish to consume at your backend.

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