Implement OAuth 2.0 refresh access token

Some OAuth providers ask to extend the access token expiration date, in
order to continue using it.
Microsoft Live do that, and it will be also soon mandatory for Facebook
because they will deprecate the 'offline_access' permission.

To refresh an access token, you need to access the accessTokenEndPoint
with other parameters like a specific 'grant_type' parameter.

src/main/java/org/scribe/builder/api/DefaultApi20.java

@@ -67,4 +67,11 @@ public OAuthService createService(OAuthConfig config)
     return new OAuth20ServiceImpl(this, config);
   }
 
+  /**
+   * @return the parameter needed to refresh a access token.
+   */
+  public String getRefreshTokenParameterName()
+  {
+    throw new UnsupportedOperationException("Refresh token is not implemented for "+getClass().getSimpleName());
+  }
 }

src/main/java/org/scribe/builder/api/FacebookApi.java

@@ -30,4 +30,10 @@ public String getAuthorizationUrl(OAuthConfig config)
       return String.format(AUTHORIZE_URL, config.getApiKey(), OAuthEncoder.encode(config.getCallback()));
     }
   }
+
+  @Override
+  public String getRefreshTokenParameterName()
+  {
+    return "fb_exchange_token";
+  }
 }

src/main/java/org/scribe/builder/api/LiveApi.java

@@ -37,4 +37,10 @@ public AccessTokenExtractor getAccessTokenExtractor()
 	{
 		return new JsonTokenExtractor();
 	}
+
+  @Override
+  public String getRefreshTokenParameterName()
+  {
+    return "refresh_token";
+  }
 }

src/main/java/org/scribe/model/OAuthConstants.java

@@ -45,5 +45,6 @@ public class OAuthConstants
   public static final String CLIENT_SECRET = "client_secret";
   public static final String REDIRECT_URI = "redirect_uri";
   public static final String CODE = "code";
+  public static final String GRANT_TYPE = "grant_type";
 
 }

src/main/java/org/scribe/oauth/OAuth10aServiceImpl.java

@@ -82,6 +82,14 @@ public Token getAccessToken(Token requestToken, Verifier verifier)
     return api.getAccessTokenExtractor().extract(response.getBody());
   }
 
+  /**
+   * {@inheritDoc}
+   */
+  public Token refreshAccessToken(Token accessToken)
+  {
+    throw new UnsupportedOperationException("Refresh token is not supported in Scribe OAuth 1.0");
+  }
+
   /**
    * {@inheritDoc}
    */

src/main/java/org/scribe/oauth/OAuth20ServiceImpl.java

@@ -37,6 +37,28 @@ public Token getAccessToken(Token requestToken, Verifier verifier)
     return api.getAccessTokenExtractor().extract(response.getBody());
   }
 
+  /**
+   * {@inheritDoc}
+   */
+  public Token refreshAccessToken(Token accessToken)
+  {
+
+    String accessTokenEndpoint = api.getAccessTokenEndpoint();
+    if (accessTokenEndpoint.contains("?grant_type="))
+    {
+      // handle the ugly case where the grant_type parameter is already hardcoded in the constant url
+      accessTokenEndpoint = accessTokenEndpoint.substring(0, accessTokenEndpoint.indexOf("?"));
+    }
+    OAuthRequest request = new OAuthRequest(api.getAccessTokenVerb(), accessTokenEndpoint);
+    request.addQuerystringParameter(OAuthConstants.CLIENT_ID, config.getApiKey());
+    request.addQuerystringParameter(OAuthConstants.CLIENT_SECRET, config.getApiSecret());
+    request.addQuerystringParameter(OAuthConstants.REDIRECT_URI, config.getCallback());
+    request.addQuerystringParameter(OAuthConstants.GRANT_TYPE, api.getRefreshTokenParameterName());
+    request.addQuerystringParameter(api.getRefreshTokenParameterName(), accessToken.getToken());
+    Response response = request.send();
+    return api.getAccessTokenExtractor().extract(response.getBody());
+  }
+
   /**
    * {@inheritDoc}
    */

src/main/java/org/scribe/oauth/OAuthService.java

@@ -27,6 +27,19 @@ public interface OAuthService
    */
   public Token getAccessToken(Token requestToken, Verifier verifier);
 
+  /**
+   * Refresh the access token to extend its expiration date.
+   * <p/>
+   * For the token in parameter, Facebook needs the access_token, while Live
+   * needs the refresh_token (which can be found only in the 
+   * {@link org.scribe.model.Token#getRawResponse()} returned by 
+   * {@link #getAccessToken(org.scribe.model.Token, org.scribe.model.Verifier)})
+   *
+   * @param accessToken access or refresh token, depending on the OAuth provider 
+   * @return fresh access token
+   */
+  public Token refreshAccessToken(Token accessToken);
+
   /**
    * Signs am OAuth request
    *