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Users need access tokens to invoke APIs subscribed under an application. Access tokens are passed in the HTTP header when invoking APIs. The API Manager provides a Token API that you can use to generate and renew user and application access tokens. The response of the Token API is a JSON message. You extract the token from the JSON and pass it with an HTTP Authorization header to access the API.

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Exchanging SAML2 bearer tokens with OAuth2 (SAML extension grant type)

SAML 2.0 is an XML-based protocol. It uses security tokens containing assertions to pass information about an end-user between a SAML authority and a SAML consumer. A SAML authority is an identity provider (IDP) and a SAML consumer is a service provider (SP).

Enterprise applications use SAML2 to engage a third-party identity provider to grant access to systems that are only authenticated against the enterprise application. These enterprise applications might need to consume OAuth-protected resources through APIs, after validating them against an OAuth2.0 authentication server. However, an enterprise application that already has a working SAML2.0 based SSO infrastructure between itself and the IDP prefers to use the existing trust relationship, even if the OAuth authorization server is entirely different from the IDP. The SAML2 Bearer Assertion Profile for OAuth2.0 leverages this existing trust relationship. It presents the SAML2.0 token to the authorization server and exchanges it to an OAuth2.0 access token.

WSO2 API Manager provides SAML2 Bearer Assertion Profile Support with the OAuth 2.0 feature. WSO2 Identity Server  (version 4.5.0 onwards) or any other SAML2 Identity provider can act as an identity service provider for the systems enabled with SSO. WSO2 API Manager acts as the OAuth authorization server. This way, an enterprise application can exchange the SAML2.0 bearer token that it retrieves when authenticating against an IDP (e.g., WSO2 Identity Server) with an OAuth2.0 access token from an OAuth authorization server (e.g., WSO2 API Manager). It can then use the OAuth2 token in API invocations.

The diagram below depicts this scenario:

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The scenarios of the above diagram are explained below:

Scenario [1]: User initiates login call to an enterprise application .

Scenario [2]:

• As the application is a SAML SP, it redirects the user to the SAML2.0 IDP to log in.
  
• The user provides credentials at the IDP and is redirected back to the SP with a SAML2.0 token signed by the IDP.
  
• The SP verifies the token and logs the user to the application.
  
• The SAML 2.0 token is stored in the user's session by the SP.  

Scenario [3]:

• The enterprise application (SP) wants to access an OAuth2 protected API resource through WSO2 API Manager.
• The application makes a request to the API Manager to exchange the SAML2 bearer token for an OAuth2.0 access token.
• The API Manager validates the assertion and returns the access token.

Scenario [4]: User does API invocations through the API Manager by setting it as an Authorization header with the returned OAuth2 access token.

Before you configure the token exchange, do the following: 

• Register to a valid user account in the API Store.
  
• Get a valid consumer key and consumer secret. Initially, these keys must be generated through the management console by clicking the Generate link on My Subscriptions page. For more information, see Invoke an API using the Integrated REST Client. 
  
• Set up a running API Gateway instance.
  
• If you have multiple WSO2 servers (such as WSO2 API Manager and WSO2 Application Server) running on the same machine, change the port offset and update the token API's endpoint accordingly. Additionally, if the key manager is on a different server from the API Gateway, update the token API endpoint to use the correct host and port. For more information, see this prerequisite in the previous section.

Let's use WSO2 Identity Server 5.0.0 as the IDP to get a SAML token and the API Manager as the OAuth server. You must get a signed SAML2 token (encoded assertion value), which you retrieve when authenticating against a SAML2 IDP. With the authentication request, you pass attributes such as SAML2 issuer name, token endpoint and the restricted audience. 

1. Log in to the API Manager's management console (https://localhost:9443/carbon) using admin/admin credentials and select Add under Identity Providers menu in the Main menu. 
   
2. Provide the following values to configure the IDP:
   
   • Under Basic Information 
     
     • Identity Provider Name: Enter a unique name for IDP
     • Identity Provider Public Certificate: Export the public certificate of WSO2 IS and import it here
     • Alias: Give the name of the alias if the Identity Provider identifies this token endpoint by an alias

   • Under Federated Authenticators -> SAML2 Web SSO Configuration

     • Enable SAML2 Web SSO: true
       

     • Identity Provider Entity Id: The SAML2 issuer name specified when generating the assertion token, which contains the unique identifier of the IDP. You give this name when configuring the SP.

     • Service Provider Entity Id: Issuer name given when configuring the SP
     • SSO URL: Enter the IDP's SAML2 Web SSO URL value. E.g., https://localhost:9444/samlsso/.
    
3. Log in to the management console of the Identity Server and provide the following values to configure the SP:
   
   • Enable Response Signing: true
   • Enable Assertion Signing: true
   • Enable Audience Restriction: true
   • Audience: URL of the token API. E.g., https://localhost:9443/oauth2/token.
      
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4. Get the SAML token using the client JAR. An example command is given below. In this command, the TestSP is the name of the issuer.
   

   Code Block
   java -jar SAML2AssertionCreator.jar TestSP admin https://localhost:9443/oauth2/token https://localhost:9443/oauth2/token/home/dinusha/nothing/WSO2/API-Manager/saml-oauth/wso2is-5.0.0/repository/resources/security/wso2carbon.jks wso2carbon wso2carbon wso2carbon

5. Get the OAuth Access token. An example command is given below.
   

   Code Block
   curl -k -d "grant_type=urn:ietf:params:oauth:grant-type:saml2-bearer&assertion=<ASSERTION_PROVIDED_BY_CLIENT>&scope=PRODUCTION" -H "Authorization: Basic <Base63 encoded consumer key:consumer secret>, Content-Type: application/x-www-form-urlencoded"https://localhost:9443/oauth2/token

Invoking Token API to generate tokens

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GenerateToken GenerateToken

  

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