feat: Add PKCE to 3LO exchange.

oauth2_http/java/com/google/auth/oauth2/DefaultPKCEProvider.java

@@ -0,0 +1,103 @@
+/*
+ * Copyright 2023, Google Inc. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *    * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *    * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *
+ *    * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package com.google.auth.oauth2;
+
+import java.security.MessageDigest;
+import java.security.NoSuchAlgorithmException;
+import java.security.SecureRandom;
+import java.util.Base64;
+
+public class DefaultPKCEProvider implements PKCEProvider {
+  private String codeVerifier;
+  private CodeChallenge codeChallenge;
+  private static final int MAX_CODE_VERIFIER_LENGTH = 127;
+
+  private class CodeChallenge {
+    private String codeChallenge;
+    private String codeChallengeMethod;
+
+    CodeChallenge(String codeVerifier) {
+      try {
+        byte[] bytes = codeVerifier.getBytes();
+        MessageDigest md = MessageDigest.getInstance("SHA-256");
+        md.update(bytes);
+
+        byte[] digest = md.digest();
+
+        this.codeChallenge = Base64.getUrlEncoder().encodeToString(digest);
+        this.codeChallengeMethod = "S256";
+      } catch (NoSuchAlgorithmException e) {
+        this.codeChallenge = codeVerifier;
+        this.codeChallengeMethod = "plain";
+      }
+    }
+
+    public String getCodeChallenge() {
+      return codeChallenge;
+    }
+
+    public String getCodeChallengeMethod() {
+      return codeChallengeMethod;
+    }
+  }
+
+  private String createCodeVerifier() {
+    SecureRandom sr = new SecureRandom();
+    byte[] code = new byte[MAX_CODE_VERIFIER_LENGTH];
+    sr.nextBytes(code);
+    return Base64.getUrlEncoder().encodeToString(code);
+  }
+
+  private CodeChallenge createCodeChallenge(String codeVerifier) {
+    return new DefaultPKCEProvider.CodeChallenge(codeVerifier);
+  }
+
+  public DefaultPKCEProvider() {
+    this.codeVerifier = createCodeVerifier();
+    this.codeChallenge = createCodeChallenge(this.codeVerifier);
+  }
+
+  @Override
+  public String getCodeVerifier() {
+    return codeVerifier;
+  }
+
+  @Override
+  public String getCodeChallenge() {
+    return codeChallenge.getCodeChallenge();
+  }
+
+  @Override
+  public String getCodeChallengeMethod() {
+    return codeChallenge.getCodeChallengeMethod();
+  }
+}

oauth2_http/java/com/google/auth/oauth2/PKCEProvider.java

@@ -0,0 +1,56 @@
+/*
+ * Copyright 2023, Google Inc. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *    * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *    * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *
+ *    * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package com.google.auth.oauth2;
+
+public interface PKCEProvider {
+  /**
+   * Get the code_challenge parameter used in PKCE.
+   *
+   * @return The code_challenge String.
+   */
+  String getCodeChallenge();
+
+  /**
+   * Get the code_challenge_method parameter used in PKCE.
+   *
+   * <p>Currently possible values are: S256,plain
+   *
+   * @return The code_challenge_method String.
+   */
+  String getCodeChallengeMethod();
+  /**
+   * Get the code_verifier parameter used in PKCE.
+   *
+   * @return The code_verifier String.
+   */
+  String getCodeVerifier();
+}

oauth2_http/java/com/google/auth/oauth2/UserAuthorizer.java

@@ -67,6 +67,7 @@ public class UserAuthorizer {
   private final HttpTransportFactory transportFactory;
   private final URI tokenServerUri;
   private final URI userAuthUri;
+  private final PKCEProvider pkce;
 
   /**
    * Constructor with all parameters.
@@ -79,6 +80,7 @@ public class UserAuthorizer {
    *     tokens.
    * @param tokenServerUri URI of the end point that provides tokens
    * @param userAuthUri URI of the Web UI for user consent
+   * @param pkce PKCE implementation
    */
   private UserAuthorizer(
       ClientId clientId,
@@ -87,7 +89,8 @@ private UserAuthorizer(
       URI callbackUri,
       HttpTransportFactory transportFactory,
       URI tokenServerUri,
-      URI userAuthUri) {
+      URI userAuthUri,
+      PKCEProvider pkce) {
     this.clientId = Preconditions.checkNotNull(clientId);
     this.scopes = ImmutableList.copyOf(Preconditions.checkNotNull(scopes));
     this.callbackUri = (callbackUri == null) ? DEFAULT_CALLBACK_URI : callbackUri;
@@ -96,6 +99,7 @@ private UserAuthorizer(
     this.tokenServerUri = (tokenServerUri == null) ? OAuth2Utils.TOKEN_SERVER_URI : tokenServerUri;
     this.userAuthUri = (userAuthUri == null) ? OAuth2Utils.USER_AUTH_URI : userAuthUri;
     this.tokenStore = (tokenStore == null) ? new MemoryTokensStorage() : tokenStore;
+    this.pkce = pkce;
   }
 
   /**
@@ -181,6 +185,10 @@ public URL getAuthorizationUrl(String userId, String state, URI baseUri) {
       url.put("login_hint", userId);
     }
     url.put("include_granted_scopes", true);
+    if (pkce != null) {
+      url.put("code_challenge", pkce.getCodeChallenge());
+      url.put("code_challenge_method", pkce.getCodeChallengeMethod());
+    }
     return url.toURL();
   }
 
@@ -248,6 +256,11 @@ public UserCredentials getCredentialsFromCode(String code, URI baseUri) throws I
     tokenData.put("client_secret", clientId.getClientSecret());
     tokenData.put("redirect_uri", resolvedCallbackUri);
     tokenData.put("grant_type", "authorization_code");
+
+    if (pkce != null) {
+      tokenData.put("code_verifier", pkce.getCodeVerifier());
+    }
+
     UrlEncodedContent tokenContent = new UrlEncodedContent(tokenData);
     HttpRequestFactory requestFactory = transportFactory.create().createRequestFactory();
     HttpRequest tokenRequest =
@@ -430,6 +443,7 @@ public static class Builder {
     private URI userAuthUri;
     private Collection<String> scopes;
     private HttpTransportFactory transportFactory;
+    private PKCEProvider pkce;
 
     protected Builder() {}
 
@@ -441,6 +455,7 @@ protected Builder(UserAuthorizer authorizer) {
       this.tokenStore = authorizer.tokenStore;
       this.callbackUri = authorizer.callbackUri;
       this.userAuthUri = authorizer.userAuthUri;
+      this.pkce = new DefaultPKCEProvider();
     }
 
     public Builder setClientId(ClientId clientId) {
@@ -478,6 +493,20 @@ public Builder setHttpTransportFactory(HttpTransportFactory transportFactory) {
       return this;
     }
 
+    public Builder setPKCEProvider(PKCEProvider pkce) {
+      if (pkce != null) {
+        if (pkce.getCodeChallenge() == null
+            || pkce.getCodeVerifier() == null
+            || pkce.getCodeChallengeMethod() == null) {
+
+          throw new IllegalArgumentException(
+              "PKCE provider contained null implementations. PKCE object must implement all PKCEProvider methods.");
+        }
+      }
+      this.pkce = pkce;
+      return this;
+    }
+
     public ClientId getClientId() {
       return clientId;
     }
@@ -506,9 +535,20 @@ public HttpTransportFactory getHttpTransportFactory() {
       return transportFactory;
     }
 
+    public PKCEProvider getPKCEProvider() {
+      return pkce;
+    }
+
     public UserAuthorizer build() {
       return new UserAuthorizer(
-          clientId, scopes, tokenStore, callbackUri, transportFactory, tokenServerUri, userAuthUri);
+          clientId,
+          scopes,
+          tokenStore,
+          callbackUri,
+          transportFactory,
+          tokenServerUri,
+          userAuthUri,
+          pkce);
     }
   }
 }

oauth2_http/javatests/com/google/auth/oauth2/DefaultPKCEProviderTest.java

@@ -0,0 +1,61 @@
+/*
+ * Copyright 2023, Google Inc. All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are
+ * met:
+ *
+ *    * Redistributions of source code must retain the above copyright
+ * notice, this list of conditions and the following disclaimer.
+ *    * Redistributions in binary form must reproduce the above
+ * copyright notice, this list of conditions and the following disclaimer
+ * in the documentation and/or other materials provided with the
+ * distribution.
+ *
+ *    * Neither the name of Google Inc. nor the names of its
+ * contributors may be used to endorse or promote products derived from
+ * this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+ * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+ * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+ * A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+ * OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+ * SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+ * LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+ * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+ * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+ * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+ * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package com.google.auth.oauth2;
+
+import static org.junit.Assert.assertEquals;
+
+import java.security.MessageDigest;
+import java.security.NoSuchAlgorithmException;
+import java.util.Base64;
+import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.JUnit4;
+
+@RunWith(JUnit4.class)
+public final class DefaultPKCEProviderTest {
+  @Test
+  public void testPkceExpected() throws NoSuchAlgorithmException {
+    PKCEProvider pkce = new DefaultPKCEProvider();
+
+    byte[] bytes = pkce.getCodeVerifier().getBytes();
+    MessageDigest md = MessageDigest.getInstance("SHA-256");
+    md.update(bytes);
+
+    byte[] digest = md.digest();
+
+    String expectedCodeChallenge = Base64.getUrlEncoder().encodeToString(digest);
+    String expectedCodeChallengeMethod = "S256";
+
+    assertEquals(pkce.getCodeChallenge(), expectedCodeChallenge);
+    assertEquals(pkce.getCodeChallengeMethod(), expectedCodeChallengeMethod);
+  }
+}

oauth2_http/javatests/com/google/auth/oauth2/UserAuthorizerTest.java

@@ -72,6 +72,7 @@ public class UserAuthorizerTest {
   private static final URI CALLBACK_URI = URI.create("/testcallback");
   private static final String CODE = "thisistheend";
   private static final URI BASE_URI = URI.create("http://example.com/foo");
+  private static final PKCEProvider pkce = new DefaultPKCEProvider();
 
   @Test
   public void constructorMinimum() {
@@ -148,6 +149,7 @@ public void getAuthorizationUrl() throws IOException {
             .setScopes(DUMMY_SCOPES)
             .setCallbackUri(CALLBACK_URI)
             .setUserAuthUri(AUTH_URI)
+            .setPKCEProvider(pkce)
             .build();
 
     URL authorizationUrl = authorizer.getAuthorizationUrl(USER_ID, CUSTOM_STATE, BASE_URI);
@@ -164,6 +166,8 @@ public void getAuthorizationUrl() throws IOException {
     assertEquals(CLIENT_ID_VALUE, parameters.get("client_id"));
     assertEquals(DUMMY_SCOPE, parameters.get("scope"));
     assertEquals("code", parameters.get("response_type"));
+    assertEquals(pkce.getCodeChallenge(), parameters.get("code_challenge"));
+    assertEquals(pkce.getCodeChallengeMethod(), parameters.get("code_challenge_method"));
   }
 
   @Test
@@ -471,4 +475,33 @@ public void revokeAuthorization_revokesAndClears() throws IOException {
     UserCredentials credentials2 = authorizer.getCredentials(USER_ID);
     assertNull(credentials2);
   }
+
+  @Test(expected = IllegalArgumentException.class)
+  public void illegalPKCEProvider() {
+    PKCEProvider pkce =
+        new PKCEProvider() {
+          @Override
+          public String getCodeVerifier() {
+            return null;
+          }
+
+          @Override
+          public String getCodeChallengeMethod() {
+            return null;
+          }
+
+          @Override
+          public String getCodeChallenge() {
+            return null;
+          }
+        };
+
+    UserAuthorizer authorizer =
+        UserAuthorizer.newBuilder()
+            .setClientId(CLIENT_ID)
+            .setScopes(DUMMY_SCOPES)
+            .setTokenStore(new MemoryTokensStorage())
+            .setPKCEProvider(pkce)
+            .build();
+  }
 }