Self-contained Access Tokens

Access tokens are credentials used to access protected resources. Typically, an access token is a string representing an authorization issued to the client. The string is usually opaque to the client.

The OAuth 2.0 specification does not mandate any particular implementation for access tokens but it  mentions  two possible strategies.

1. The access token is an identifier that is hard to guess. For example, a randomly generated string of sufficient length, that the server handling the protected resource can use to lookup the associated authorization information.

2. The access token self-contains the authorization information in a manner that can be verified. For example, by encoding authorization information along with a signature into the token.

So by default, a UUID is issued as an access token in WSO2 Identity Server, which is of the first type above. But, it also can be configured to issue a self-contained access token, which is of the second type above.

When short string identifiers are used as access tokens, a network request to the Authorization server is required to retrieve the authorization information associated with each access token. But with self-contained access tokens there is no need for a network call to retrieve the authorization information, as it’s self-contained. Thus, access token processing may be significantly quicker and more efficient. However, when it comes to token revocation self-contained access tokens lag, whereas access tokens with string identifiers can be revoked with almost immediate effect. The common practice is to have a short expiration time with self-contained access tokens, but that may result in more refresh token requests at the Authorization server.

WSO2 Identity Server needs to be configured to issue above explained self-contained JWT access tokens as below.

1. Open the <IS_HOME>/repository/conf/identity/identity.xml file and uncomment the following entry under <OAuth> element.

   <IdentityOAuthTokenGenerator>org.wso2.carbon.identity.oauth2.token.JWTTokenIssuer</IdentityOAuthTokenGenerator>

2. Restart the server.

3. Configure an OAuth service provider.

4. Initiate an access token request to the WSO2 Identity Server, over a known grant type. For example, the following cURL command illustrates the syntax of an access token request that can be initiated over the Resource Owner Password Credential grant type.