[JAVA][Feign] Replace Apache oltu with scribejava (#8318)

* - Replace apache oltu with scribejava - Implement the following authentication methods - ApiKey header - HTTP basic authentication - Oauth client credentials flow - Oauth Implicit flow - Oauth Pasword (deprecated) * Create class hierarchy for Oauth flows implementation * Add instructions of how to use the ApiClient to Readme.md * Update samples * Remove support for java 6 and 7 * Remove java 6 and 7 support from gradle * Format pom.xml * Remove empty line * Update samples * Remove oltu dependency from build.gradle and build.sbt. Replace oltu with ScribeJava Update samples * Update samples * Update samples
2021-01-19 04:41:25 +00:00
parent 6e4c1307a7
commit ede2a2316c
43 changed files with 1208 additions and 1211 deletions
--- a/samples/client/petstore/java/feign-no-nullable/src/main/java/org/openapitools/client/ApiClient.java
+++ b/samples/client/petstore/java/feign-no-nullable/src/main/java/org/openapitools/client/ApiClient.java
@@ -2,9 +2,8 @@ package org.openapitools.client;

 import java.util.LinkedHashMap;
 import java.util.Map;
-
-import org.apache.oltu.oauth2.client.request.OAuthClientRequest.AuthenticationRequestBuilder;
-import org.apache.oltu.oauth2.client.request.OAuthClientRequest.TokenRequestBuilder;
+import java.util.logging.Level;
+import java.util.logging.Logger;

 import org.threeten.bp.*;

@@ -24,6 +23,8 @@ import org.openapitools.client.auth.OAuth.AccessTokenListener;

@javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen")
 public class ApiClient {
+  private static final Logger log = Logger.getLogger(ApiClient.class.getName());
+
  public interface Api {}

  protected ObjectMapper objectMapper;
@@ -43,6 +44,7 @@ public class ApiClient {
  public ApiClient(String[] authNames) {
    this();
    for(String authName : authNames) {
+      log.log(Level.FINE, "Creating authentication {0}", authName);
      RequestInterceptor auth;
      if ("api_key".equals(authName)) {
        auth = new ApiKeyAuth("header", "api_key");
@@ -51,7 +53,7 @@ public class ApiClient {
      } else if ("http_basic_test".equals(authName)) {
        auth = new HttpBasicAuth();
      } else if ("petstore_auth".equals(authName)) {
-        auth = new OAuth(OAuthFlow.implicit, "http://petstore.swagger.io/api/oauth/dialog", "", "write:pets, read:pets");
+        auth = buildOauthRequestInterceptor(OAuthFlow.implicit, "http://petstore.swagger.io/api/oauth/dialog", "", "write:pets, read:pets");
      } else {
        throw new RuntimeException("auth name \"" + authName + "\" not found in available auth names");
      }
@@ -77,34 +79,6 @@ public class ApiClient {
    this.setApiKey(apiKey);
  }

-  /**
-   * Helper constructor for single basic auth or password oauth2
-   * @param authName
-   * @param username
-   * @param password
-   */
-  public ApiClient(String authName, String username, String password) {
-    this(authName);
-    this.setCredentials(username,  password);
-  }
-
-  /**
-   * Helper constructor for single password oauth2
-   * @param authName
-   * @param clientId
-   * @param secret
-   * @param username
-   * @param password
-   */
-  public ApiClient(String authName, String clientId, String secret, String username, String password) {
-    this(authName);
-    this.getTokenEndPoint()
-           .setClientId(clientId)
-           .setClientSecret(secret)
-           .setUsername(username)
-           .setPassword(password);
-  }
-
  public String getBasePath() {
    return basePath;
  }
@@ -147,10 +121,25 @@ public class ApiClient {
    return objectMapper;
  }

+  private RequestInterceptor buildOauthRequestInterceptor(OAuthFlow flow, String authorizationUrl, String tokenUrl, String scopes) {
+    switch (flow) {
+      case password:
+        return new OauthPasswordGrant(tokenUrl, scopes);
+      case application:
+        return new OauthClientCredentialsGrant(authorizationUrl, tokenUrl, scopes);
+      default:
+        throw new RuntimeException("Oauth flow \"" + flow + "\" is not implemented");
+    }
+  }
+
  public ObjectMapper getObjectMapper(){
    return objectMapper;
  }

+  public void setObjectMapper(ObjectMapper objectMapper) {
+        this.objectMapper = objectMapper;
+  }
+
  /**
   * Creates a feign client for given API interface.
   *
@@ -197,19 +186,13 @@ public class ApiClient {
    return contentTypes[0];
  }

-
  /**
   * Helper method to configure the bearer token.
   * @param bearerToken the bearer token.
   */
  public void setBearerToken(String bearerToken) {
-    for(RequestInterceptor apiAuthorization : apiAuthorizations.values()) {
-      if (apiAuthorization instanceof HttpBearerAuth) {
-        ((HttpBearerAuth) apiAuthorization).setBearerToken(bearerToken);
-        return;
-      }
-    }
-    throw new RuntimeException("No Bearer authentication configured!");
+    HttpBearerAuth apiAuthorization =  getAuthorization(HttpBearerAuth.class);
+    apiAuthorization.setBearerToken(bearerToken);
  }

  /**
@@ -217,63 +200,38 @@ public class ApiClient {
   * @param apiKey API key
   */
  public void setApiKey(String apiKey) {
-    for(RequestInterceptor apiAuthorization : apiAuthorizations.values()) {
-      if (apiAuthorization instanceof ApiKeyAuth) {
-        ApiKeyAuth keyAuth = (ApiKeyAuth) apiAuthorization;
-        keyAuth.setApiKey(apiKey);
-        return ;
-      }
-    }
-    throw new RuntimeException("No API key authentication configured!");
+    ApiKeyAuth apiAuthorization =  getAuthorization(ApiKeyAuth.class);
+    apiAuthorization.setApiKey(apiKey);
  }

  /**
-   * Helper method to configure the username/password for basic auth or password OAuth
+   * Helper method to configure the username/password for basic auth
   * @param username Username
   * @param password Password
   */
  public void setCredentials(String username, String password) {
-    for(RequestInterceptor apiAuthorization : apiAuthorizations.values()) {
-      if (apiAuthorization instanceof HttpBasicAuth) {
-        HttpBasicAuth basicAuth = (HttpBasicAuth) apiAuthorization;
-        basicAuth.setCredentials(username, password);
-        return;
-      }
-      if (apiAuthorization instanceof OAuth) {
-        OAuth oauth = (OAuth) apiAuthorization;
-        oauth.getTokenRequestBuilder().setUsername(username).setPassword(password);
-        return;
-      }
-    }
-    throw new RuntimeException("No Basic authentication or OAuth configured!");
+    HttpBasicAuth apiAuthorization = getAuthorization(HttpBasicAuth.class);
+    apiAuthorization.setCredentials(username, password);
  }

  /**
-   * Helper method to configure the token endpoint of the first oauth found in the apiAuthorizations (there should be only one)
-   * @return Token request builder
+   * Helper method to configure the client credentials for Oauth 
+   * @param username Username
+   * @param password Password
   */
-  public TokenRequestBuilder getTokenEndPoint() {
-    for(RequestInterceptor apiAuthorization : apiAuthorizations.values()) {
-      if (apiAuthorization instanceof OAuth) {
-        OAuth oauth = (OAuth) apiAuthorization;
-        return oauth.getTokenRequestBuilder();
-      }
-    }
-    return null;
+  public void setClientCredentials(String clientId, String clientSecret) {
+    OauthClientCredentialsGrant authorization = getAuthorization(OauthClientCredentialsGrant.class);
+    authorization.configure(clientId, clientSecret);
  }

  /**
-   * Helper method to configure authorization endpoint of the first oauth found in the apiAuthorizations (there should be only one)
-   * @return Authentication request builder
+   * Helper method to configure the username/password for Oauth password grant
+   * @param username Username
+   * @param password Password
   */
-  public AuthenticationRequestBuilder getAuthorizationEndPoint() {
-    for(RequestInterceptor apiAuthorization : apiAuthorizations.values()) {
-      if (apiAuthorization instanceof OAuth) {
-        OAuth oauth = (OAuth) apiAuthorization;
-        return oauth.getAuthenticationRequestBuilder();
-      }
-    }
-    return null;
+  public void setOauthPassword(String username, String password, String clientId, String clientSecret) {
+    OauthPasswordGrant apiAuthorization = getAuthorization(OauthPasswordGrant.class);
+    apiAuthorization.configure(username, password, clientId, clientSecret);
  }

  /**
@@ -281,14 +239,9 @@ public class ApiClient {
   * @param accessToken Access Token
   * @param expiresIn Validity period in seconds
   */
-  public void setAccessToken(String accessToken, Long expiresIn) {
-    for(RequestInterceptor apiAuthorization : apiAuthorizations.values()) {
-      if (apiAuthorization instanceof OAuth) {
-        OAuth oauth = (OAuth) apiAuthorization;
-        oauth.setAccessToken(accessToken, expiresIn);
-        return;
-      }
-    }
+  public void setAccessToken(String accessToken, Integer expiresIn) {
+    OAuth apiAuthorization = getAuthorization(OAuth.class);
+    apiAuthorization.setAccessToken(accessToken, expiresIn);
  }

  /**
@@ -298,19 +251,7 @@ public class ApiClient {
   * @param redirectURI Redirect URI
   */
  public void configureAuthorizationFlow(String clientId, String clientSecret, String redirectURI) {
-    for(RequestInterceptor apiAuthorization : apiAuthorizations.values()) {
-      if (apiAuthorization instanceof OAuth) {
-        OAuth oauth = (OAuth) apiAuthorization;
-        oauth.getTokenRequestBuilder()
-                .setClientId(clientId)
-                .setClientSecret(clientSecret)
-                .setRedirectURI(redirectURI);
-        oauth.getAuthenticationRequestBuilder()
-                .setClientId(clientId)
-                .setRedirectURI(redirectURI);
-        return;
-      }
-    }
+    throw new RuntimeException("Not implemented");
  }

  /**
@@ -318,13 +259,8 @@ public class ApiClient {
   * @param accessTokenListener Acesss token listener
   */
  public void registerAccessTokenListener(AccessTokenListener accessTokenListener) {
-    for(RequestInterceptor apiAuthorization : apiAuthorizations.values()) {
-      if (apiAuthorization instanceof OAuth) {
-        OAuth oauth = (OAuth) apiAuthorization;
-        oauth.registerAccessTokenListener(accessTokenListener);
-        return;
-      }
-    }
+    OAuth apiAuthorization = getAuthorization(OAuth.class);
+    apiAuthorization.registerAccessTokenListener(accessTokenListener);
  }

  /**
@@ -349,4 +285,11 @@ public class ApiClient {
    feignBuilder.requestInterceptor(authorization);
  }

+  private <T extends RequestInterceptor> T getAuthorization(Class<T> type) {
+    return (T) apiAuthorizations.values()
+                                .stream()
+                                .filter(requestInterceptor -> type.isAssignableFrom(requestInterceptor.getClass()))
+                                .findFirst()
+                                .orElseThrow(() -> new RuntimeException("No Oauth authentication or OAuth configured!"));
+    }
 }
--- a/samples/client/petstore/java/feign-no-nullable/src/main/java/org/openapitools/client/auth/DefaultApi20Impl.java
+++ b/samples/client/petstore/java/feign-no-nullable/src/main/java/org/openapitools/client/auth/DefaultApi20Impl.java
@@ -0,0 +1,47 @@
+package org.openapitools.client.auth;
+
+import com.github.scribejava.core.builder.api.DefaultApi20;
+import com.github.scribejava.core.extractors.OAuth2AccessTokenJsonExtractor;
+import com.github.scribejava.core.extractors.TokenExtractor;
+import com.github.scribejava.core.model.OAuth2AccessToken;
+import com.github.scribejava.core.oauth2.bearersignature.BearerSignature;
+import com.github.scribejava.core.oauth2.bearersignature.BearerSignatureURIQueryParameter;
+import com.github.scribejava.core.oauth2.clientauthentication.ClientAuthentication;
+import com.github.scribejava.core.oauth2.clientauthentication.RequestBodyAuthenticationScheme;
+
+@javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen")
+public class DefaultApi20Impl extends DefaultApi20 {
+
+    private final String accessTokenEndpoint;
+    private final String authorizationBaseUrl;
+
+    protected DefaultApi20Impl(String authorizationBaseUrl, String accessTokenEndpoint) {
+        this.authorizationBaseUrl = authorizationBaseUrl;
+        this.accessTokenEndpoint = accessTokenEndpoint;
+    }
+
+    @Override
+    public String getAccessTokenEndpoint() {
+        return accessTokenEndpoint;
+    }
+
+    @Override
+    protected String getAuthorizationBaseUrl() {
+        return authorizationBaseUrl;
+    }
+
+    @Override
+    public BearerSignature getBearerSignature() {
+        return BearerSignatureURIQueryParameter.instance();
+    }
+
+    @Override
+    public ClientAuthentication getClientAuthentication() {
+        return RequestBodyAuthenticationScheme.instance();
+    }
+
+    @Override
+    public TokenExtractor<OAuth2AccessToken> getAccessTokenExtractor() {
+        return OAuth2AccessTokenJsonExtractor.instance();
+    }
+}
--- a/samples/client/petstore/java/feign-no-nullable/src/main/java/org/openapitools/client/auth/OAuth.java
+++ b/samples/client/petstore/java/feign-no-nullable/src/main/java/org/openapitools/client/auth/OAuth.java
@@ -1,198 +1,81 @@
 package org.openapitools.client.auth;

-import java.io.IOException;
-import java.util.Collection;
-import java.util.Map;
-import java.util.Map.Entry;
-
-import org.apache.oltu.oauth2.client.HttpClient;
-import org.apache.oltu.oauth2.client.OAuthClient;
-import org.apache.oltu.oauth2.client.request.OAuthClientRequest;
-import org.apache.oltu.oauth2.client.request.OAuthClientRequest.AuthenticationRequestBuilder;
-import org.apache.oltu.oauth2.client.request.OAuthClientRequest.TokenRequestBuilder;
-import org.apache.oltu.oauth2.client.response.OAuthClientResponse;
-import org.apache.oltu.oauth2.client.response.OAuthClientResponseFactory;
-import org.apache.oltu.oauth2.client.response.OAuthJSONAccessTokenResponse;
-import org.apache.oltu.oauth2.common.exception.OAuthProblemException;
-import org.apache.oltu.oauth2.common.exception.OAuthSystemException;
-import org.apache.oltu.oauth2.common.message.types.GrantType;
-import org.apache.oltu.oauth2.common.token.BasicOAuthToken;
-
-import feign.Client;
+import com.github.scribejava.core.model.OAuth2AccessToken;
+import com.github.scribejava.core.oauth.OAuth20Service;
 import feign.Request.HttpMethod;
-import feign.Request.Options;
 import feign.RequestInterceptor;
 import feign.RequestTemplate;
-import feign.Response;
 import feign.RetryableException;
-import feign.Util;
-import org.openapitools.client.StringUtil;

+@javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen")
+public abstract class OAuth implements RequestInterceptor {

-public class OAuth implements RequestInterceptor {
+  static final int MILLIS_PER_SECOND = 1000;

-    static final int MILLIS_PER_SECOND = 1000;
+  public interface AccessTokenListener {
+    void notify(OAuth2AccessToken token);
+  }

-    public interface AccessTokenListener {
-        void notify(BasicOAuthToken token);
+  private volatile String accessToken;
+  private Long expirationTimeMillis;
+  private AccessTokenListener accessTokenListener;
+
+  protected OAuth20Service service;
+  protected String scopes;
+  protected String authorizationUrl;
+  protected String tokenUrl;
+
+  public OAuth(String authorizationUrl, String tokenUrl, String scopes) {
+    this.scopes = scopes;
+    this.authorizationUrl = authorizationUrl;
+    this.tokenUrl = tokenUrl;
+  }
+
+  @Override
+  public void apply(RequestTemplate template) {
+    // If the request already have an authorization (eg. Basic auth), do nothing
+    if (template.headers().containsKey("Authorization")) {
+      return;
    }
-
-    private volatile String accessToken;
-    private Long expirationTimeMillis;
-    private OAuthClient oauthClient;
-    private TokenRequestBuilder tokenRequestBuilder;
-    private AuthenticationRequestBuilder authenticationRequestBuilder;
-    private AccessTokenListener accessTokenListener;
-
-    public OAuth(Client client, TokenRequestBuilder requestBuilder) {
-        this.oauthClient = new OAuthClient(new OAuthFeignClient(client));
-        this.tokenRequestBuilder = requestBuilder;
+    // If first time, get the token
+    if (expirationTimeMillis == null || System.currentTimeMillis() >= expirationTimeMillis) {
+      updateAccessToken(template);
    }
-
-    public OAuth(Client client, OAuthFlow flow, String authorizationUrl, String tokenUrl, String scopes) {
-        this(client, OAuthClientRequest.tokenLocation(tokenUrl).setScope(scopes));
-
-        switch(flow) {
-        case accessCode:
-        case implicit:
-            tokenRequestBuilder.setGrantType(GrantType.AUTHORIZATION_CODE);
-            break;
-        case password:
-            tokenRequestBuilder.setGrantType(GrantType.PASSWORD);
-            break;
-        case application:
-            tokenRequestBuilder.setGrantType(GrantType.CLIENT_CREDENTIALS);
-            break;
-        default:
-            break;
-        }
-        authenticationRequestBuilder = OAuthClientRequest.authorizationLocation(authorizationUrl);
+    if (getAccessToken() != null) {
+      template.header("Authorization", "Bearer " + getAccessToken());
    }
+  }

-    public OAuth(OAuthFlow flow, String authorizationUrl, String tokenUrl, String scopes) {
-        this(new Client.Default(null, null), flow, authorizationUrl, tokenUrl, scopes);
+  private synchronized void updateAccessToken(RequestTemplate template) {
+    OAuth2AccessToken accessTokenResponse;
+    try {
+      accessTokenResponse = getOAuth2AccessToken();
+    } catch (Exception e) {
+      throw new RetryableException(0, e.getMessage(), HttpMethod.POST, e, null, template.request());
    }
-
-    @Override
-    public void apply(RequestTemplate template) {
-        // If the request already have an authorization (eg. Basic auth), do nothing
-        if (template.headers().containsKey("Authorization")) {
-            return;
-        }
-        // If first time, get the token
-        if (expirationTimeMillis == null || System.currentTimeMillis() >= expirationTimeMillis) {
-            updateAccessToken(template);
-        }
-        if (getAccessToken() != null) {
-            template.header("Authorization", "Bearer " + getAccessToken());
-        }
+    if (accessTokenResponse != null && accessTokenResponse.getAccessToken() != null) {
+      setAccessToken(accessTokenResponse.getAccessToken(), accessTokenResponse.getExpiresIn());
+      if (accessTokenListener != null) {
+        accessTokenListener.notify(accessTokenResponse);
+      }
    }
+  }

-    public synchronized void updateAccessToken(RequestTemplate template) {
-        OAuthJSONAccessTokenResponse accessTokenResponse;
-        try {
-            accessTokenResponse = oauthClient.accessToken(tokenRequestBuilder.buildBodyMessage());
-        } catch (Exception e) {
-            throw new RetryableException(0, e.getMessage(), HttpMethod.POST, e, null, template.request());
-        }
-        if (accessTokenResponse != null && accessTokenResponse.getAccessToken() != null) {
-            setAccessToken(accessTokenResponse.getAccessToken(), accessTokenResponse.getExpiresIn());
-            if (accessTokenListener != null) {
-                accessTokenListener.notify((BasicOAuthToken) accessTokenResponse.getOAuthToken());
-            }
-        }
-    }
+  abstract OAuth2AccessToken getOAuth2AccessToken();

-    public synchronized void registerAccessTokenListener(AccessTokenListener accessTokenListener) {
-        this.accessTokenListener = accessTokenListener;
-    }
+  abstract OAuthFlow getFlow();

-    public synchronized String getAccessToken() {
-        return accessToken;
-    }
+  public synchronized void registerAccessTokenListener(AccessTokenListener accessTokenListener) {
+    this.accessTokenListener = accessTokenListener;
+  }

-    public synchronized void setAccessToken(String accessToken, Long expiresIn) {
-        this.accessToken = accessToken;
-        this.expirationTimeMillis = expiresIn == null ? null : System.currentTimeMillis() + expiresIn * MILLIS_PER_SECOND;
-    }
+  public synchronized String getAccessToken() {
+    return accessToken;
+  }

-    public TokenRequestBuilder getTokenRequestBuilder() {
-        return tokenRequestBuilder;
-    }
+  public synchronized void setAccessToken(String accessToken, Integer expiresIn) {
+    this.accessToken = accessToken;
+    this.expirationTimeMillis = expiresIn == null ? null : System.currentTimeMillis() + expiresIn * MILLIS_PER_SECOND;
+  }

-    public void setTokenRequestBuilder(TokenRequestBuilder tokenRequestBuilder) {
-        this.tokenRequestBuilder = tokenRequestBuilder;
-    }
-
-    public AuthenticationRequestBuilder getAuthenticationRequestBuilder() {
-        return authenticationRequestBuilder;
-    }
-
-    public void setAuthenticationRequestBuilder(AuthenticationRequestBuilder authenticationRequestBuilder) {
-        this.authenticationRequestBuilder = authenticationRequestBuilder;
-    }
-
-    public OAuthClient getOauthClient() {
-        return oauthClient;
-    }
-
-    public void setOauthClient(OAuthClient oauthClient) {
-        this.oauthClient = oauthClient;
-    }
-
-    public void setOauthClient(Client client) {
-        this.oauthClient = new OAuthClient( new OAuthFeignClient(client));
-    }
-
-    public static class OAuthFeignClient implements HttpClient {
-
-        private Client client;
-
-        public OAuthFeignClient() {
-            this.client = new Client.Default(null, null);
-        }
-
-        public OAuthFeignClient(Client client) {
-            this.client = client;
-        }
-
-        public <T extends OAuthClientResponse> T execute(OAuthClientRequest request, Map<String, String> headers,
-                String requestMethod, Class<T> responseClass)
-                        throws OAuthSystemException, OAuthProblemException {
-
-            RequestTemplate req = new RequestTemplate()
-                    .append(request.getLocationUri())
-                    .method(requestMethod)
-                    .body(request.getBody());
-
-            for (Entry<String, String> entry : headers.entrySet()) {
-                req.header(entry.getKey(), entry.getValue());
-            }
-            Response feignResponse;
-            String body = "";
-            try {
-                feignResponse = client.execute(req.request(), new Options());
-                body = Util.toString(feignResponse.body().asReader());
-            } catch (IOException e) {
-                throw new OAuthSystemException(e);
-            }
-
-            String contentType = null;
-            Collection<String> contentTypeHeader =  feignResponse.headers().get("Content-Type");
-            if(contentTypeHeader != null) {
-                contentType = StringUtil.join(contentTypeHeader.toArray(new String[0]), ";");
-            }
-
-            return OAuthClientResponseFactory.createCustomResponse(
-                    body,
-                    contentType,
-                    feignResponse.status(),
-                    responseClass
-            );
-        }
-
-        public void shutdown() {
-            // Nothing to do here
-        }
-    }
-}
+}
--- a/samples/client/petstore/java/feign-no-nullable/src/main/java/org/openapitools/client/auth/OAuthFlow.java
+++ b/samples/client/petstore/java/feign-no-nullable/src/main/java/org/openapitools/client/auth/OAuthFlow.java
@@ -13,6 +13,10 @@

 package org.openapitools.client.auth;

+@javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen")
 public enum OAuthFlow {
-    accessCode, implicit, password, application
+    accessCode, //called authorizationCode  in OpenAPI 3.0
+    implicit, 
+    password,
+    application //called clientCredentials in OpenAPI 3.0
 }
--- a/samples/client/petstore/java/feign-no-nullable/src/main/java/org/openapitools/client/auth/OauthClientCredentialsGrant.java
+++ b/samples/client/petstore/java/feign-no-nullable/src/main/java/org/openapitools/client/auth/OauthClientCredentialsGrant.java
@@ -0,0 +1,39 @@
+package org.openapitools.client.auth;
+
+import com.github.scribejava.core.builder.ServiceBuilder;
+import com.github.scribejava.core.model.OAuth2AccessToken;
+
+@javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen")
+public class OauthClientCredentialsGrant extends OAuth {
+
+  public OauthClientCredentialsGrant(String authorizationUrl, String tokenUrl, String scopes) {
+    super(authorizationUrl, tokenUrl, scopes);
+  }
+
+  @Override
+  protected OAuth2AccessToken getOAuth2AccessToken() {
+    try {
+      return service.getAccessTokenClientCredentialsGrant(scopes);
+    } catch (Exception e) {
+      throw new RuntimeException("Failed to get oauth token", e);
+    }
+  }
+
+  @Override
+  protected OAuthFlow getFlow() {
+    return OAuthFlow.application;
+  }
+
+  /**
+   * Configures the client credentials flow
+   *
+   * @param clientId
+   * @param clientSecret
+   */
+  public void configure(String clientId, String clientSecret) {
+    service = new ServiceBuilder(clientId)
+            .apiSecret(clientSecret)
+            .defaultScope(scopes)
+            .build(new DefaultApi20Impl(authorizationUrl, tokenUrl));
+  }
+}
--- a/samples/client/petstore/java/feign-no-nullable/src/main/java/org/openapitools/client/auth/OauthPasswordGrant.java
+++ b/samples/client/petstore/java/feign-no-nullable/src/main/java/org/openapitools/client/auth/OauthPasswordGrant.java
@@ -0,0 +1,48 @@
+package org.openapitools.client.auth;
+
+import com.github.scribejava.core.builder.ServiceBuilder;
+import com.github.scribejava.core.model.OAuth2AccessToken;
+
+@javax.annotation.Generated(value = "org.openapitools.codegen.languages.JavaClientCodegen")
+public class OauthPasswordGrant extends OAuth {
+
+  private String username;
+  private String password;
+
+  public OauthPasswordGrant(String tokenUrl, String scopes) {
+    super(null, tokenUrl, scopes);
+  }
+
+  @Override
+  protected OAuth2AccessToken getOAuth2AccessToken() {
+    try {
+      return service.getAccessTokenPasswordGrant(username, password);
+    } catch (Exception e) {
+      throw new RuntimeException("Failed to get oauth token", e);
+    }
+  }
+
+  @Override
+  protected OAuthFlow getFlow() {
+    return OAuthFlow.password;
+  }
+
+  /**
+   * Configures Oauth password grant flow
+   * Note: this flow is deprecated.
+   *
+   * @param username
+   * @param password
+   * @param clientId
+   * @param clientSecret
+   */
+  public void configure(String username, String password, String clientId, String clientSecret) {
+    this.username = username;
+    this.password = password;
+    //TODO the clientId and secret are optional according with the RFC
+    service = new ServiceBuilder(clientId)
+            .apiSecret(clientSecret)
+            .defaultScope(scopes)
+            .build(new DefaultApi20Impl(authorizationUrl, tokenUrl));
+  }
+}