@@ -0,0 +1,64 @@
+/*
+* Copyright 2021 Google LLC
+*
+* Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
+* in compliance with the License. You may obtain a copy of the License at
+*
+* http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software distributed under the License
+* is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
+* or implied. See the License for the specific language governing permissions and limitations under
+* the License.
+*/
+
+package com.google.api.client.auth.oauth;
+
+import com.google.api.client.util.StringUtils;
+import com.google.common.io.BaseEncoding;
+import java.security.GeneralSecurityException;
+import javax.crypto.Mac;
+import javax.crypto.SecretKey;
+import javax.crypto.spec.SecretKeySpec;
+
+/** OAuth {@code "HMAC-SHA256"} signature method. */
+public final class OAuthHmacSha256Signer implements OAuthSigner {
+
+/** Client secret */
+private final String clientSharedSecret;
+
+/** Token secret */
+private String tokenSharedSecret;
+
+public void setTokenSecret(String tokenSecret) {
+tokenSharedSecret = tokenSecret;
+}
+
+public OAuthHmacSha256Signer(String clientSecret) {
+this.clientSharedSecret = clientSecret;
+}
+
+@Override
+public String getSignatureMethod() {
+return "HMAC-SHA256";
+}
+
+@Override
+public String computeSignature(String signatureBaseString) throws GeneralSecurityException {
+// compute key
+StringBuilder keyBuffer = new StringBuilder();
+if (clientSharedSecret != null) {
+keyBuffer.append(OAuthParameters.escape(clientSharedSecret));
+}
+keyBuffer.append('&');
+if (tokenSharedSecret != null) {
+keyBuffer.append(OAuthParameters.escape(tokenSharedSecret));
+}
+String key = keyBuffer.toString();
+// sign
+SecretKey secretKey = new SecretKeySpec(StringUtils.getBytesUtf8(key), "HmacSHA256");
+Mac mac = Mac.getInstance("HmacSHA256");
+mac.init(secretKey);
+return BaseEncoding.base64().encode(mac.doFinal(StringUtils.getBytesUtf8(signatureBaseString)));
+}
+}

@@ -0,0 +1,54 @@
+/*
+* Copyright 2021 Google LLC
+*
+* Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
+* in compliance with the License. You may obtain a copy of the License at
+*
+* http://www.apache.org/licenses/LICENSE-2.0
+*
+* Unless required by applicable law or agreed to in writing, software distributed under the License
+* is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express
+* or implied. See the License for the specific language governing permissions and limitations under
+* the License.
+*/
+
+package com.google.api.client.auth.oauth;
+
+import static org.junit.Assert.assertEquals;
+
+import java.security.GeneralSecurityException;
+import org.junit.Test;
+
+/** Tests {@link OAuthHmacSha256Signer}. */
+public class OAuthHmacSha256SignerTest {
+
+@Test
+public void testComputeSignatureWithNullSecrets() throws GeneralSecurityException {
+OAuthHmacSha256Signer signer = new OAuthHmacSha256Signer(null);
+String expectedSignature = "l/Es58FI4BtBciSH9XtY/5jXFee70v7/rPiQgEpvv00=";
+assertEquals(expectedSignature, signer.computeSignature("baseString"));
+}
+
+@Test
+public void testComputeSignatureWithNullClientSecret() throws GeneralSecurityException {
+OAuthHmacSha256Signer signer = new OAuthHmacSha256Signer(null);
+signer.setTokenSecret("tokenSecret");
+String expectedSignature = "PgNWY2qQ53qvk3WySct/f037/usxMGpNDjmJeISmgCM=";
+assertEquals(expectedSignature, signer.computeSignature("baseString"));
+}
+
+@Test
+public void testComputeSignatureWithNullTokenSecret() throws GeneralSecurityException {
+OAuthHmacSha256Signer signer = new OAuthHmacSha256Signer("clientSecret");
+String expectedSignature = "cNrT2sqgyQ+dd7rbAhYBFBk8o82/yZyZkavqsfMDqpo=";
+assertEquals(expectedSignature, signer.computeSignature("baseString"));
+}
+
+@Test
+public void testComputeSignature() throws GeneralSecurityException {
+OAuthHmacSha256Signer signer = new OAuthHmacSha256Signer("clientSecret");
+signer.setTokenSecret("tokenSecret");
+String expectedSignature = "sfnrBcfwccOs2mpc60VQ5zXx5ReP/46lgUcBhU2a4PM=";
+assertEquals(expectedSignature, signer.computeSignature("baseString"));
+}
+}