fix: environment variable is "AWS_SESSION_TOKEN" and not "Token" (googleapis#772)

Author: lsirac

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

@@ -273,7 +273,7 @@ AwsSecurityCredentials getAwsSecurityCredentials() throws IOException {
     // Check environment variables for credentials first.
     String accessKeyId = getEnvironmentProvider().getEnv("AWS_ACCESS_KEY_ID");
     String secretAccessKey = getEnvironmentProvider().getEnv("AWS_SECRET_ACCESS_KEY");
-    String token = getEnvironmentProvider().getEnv("Token");
+    String token = getEnvironmentProvider().getEnv("AWS_SESSION_TOKEN");
     if (accessKeyId != null && secretAccessKey != null) {
       return new AwsSecurityCredentials(accessKeyId, secretAccessKey, token);
     }

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

@@ -276,7 +276,7 @@ void getAwsSecurityCredentials_fromEnvironmentVariablesWithToken() throws IOExce
     environmentProvider
         .setEnv("AWS_ACCESS_KEY_ID", "awsAccessKeyId")
         .setEnv("AWS_SECRET_ACCESS_KEY", "awsSecretAccessKey")
-        .setEnv("Token", "token");
+        .setEnv("AWS_SESSION_TOKEN", "awsSessionToken");
 
     AwsCredentials testAwsCredentials =
         (AwsCredentials)
@@ -288,7 +288,7 @@ void getAwsSecurityCredentials_fromEnvironmentVariablesWithToken() throws IOExce
 
     assertEquals("awsAccessKeyId", credentials.getAccessKeyId());
     assertEquals("awsSecretAccessKey", credentials.getSecretAccessKey());
-    assertEquals("token", credentials.getToken());
+    assertEquals("awsSessionToken", credentials.getToken());
   }
 
   @Test

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

@@ -535,9 +535,9 @@ public AwsSecurityCredentials retrieveAwsSecurityCredentials() throws IOExceptio
 
     GenericJson json = parser.parseAndClose(stream, StandardCharsets.UTF_8, GenericJson.class);
 
-    String awsToken = (String) json.get("Token");
-    String secretAccessKey = (String) json.get("SecretAccessKey");
     String accessKeyId = (String) json.get("AccessKeyId");
+    String secretAccessKey = (String) json.get("SecretAccessKey");
+    String awsToken = (String) json.get("Token");
 
     return new AwsSecurityCredentials(accessKeyId, secretAccessKey, awsToken);
   }

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

@@ -138,7 +138,7 @@ void awsCredentials() throws Exception {
     testEnvironmentProvider
         .setEnv("AWS_ACCESS_KEY_ID", awsAccessKeyId)
         .setEnv("AWS_SECRET_ACCESS_KEY", awsSecretAccessKey)
-        .setEnv("Token", awsSessionToken)
+        .setEnv("AWS_SESSION_TOKEN", awsSessionToken)
         .setEnv("AWS_REGION", "us-east-2");
 
     AwsCredentials awsCredential =