alts: Ignore case when matching the peer service account

alts/src/main/java/io/grpc/alts/AuthorizationUtil.java

@@ -29,8 +29,8 @@ private AuthorizationUtil() {}
 
   /**
    * Given a server call, performs client authorization check, i.e., checks if the client service
-   * account matches one of the expected service accounts. It returns OK if client is authorized and
-   * an error otherwise.
+   * account matches one of the expected service accounts, ignoring case. It returns OK if client
+   * is authorized and an error otherwise.
    */
   public static Status clientAuthorizationCheck(
       ServerCall<?, ?> call, Collection<String> expectedServiceAccounts) {
@@ -39,10 +39,13 @@ public static Status clientAuthorizationCheck(
     if (altsContext == null) {
       return Status.PERMISSION_DENIED.withDescription("Peer ALTS AuthContext not found");
     }
-    if (expectedServiceAccounts.contains(altsContext.getPeerServiceAccount())) {
-      return Status.OK;
+    String peerServiceAccount = altsContext.getPeerServiceAccount();
+    for (String serviceAccount : expectedServiceAccounts) {
+      if (peerServiceAccount.equalsIgnoreCase(serviceAccount)) {
+        return Status.OK;
+      }
     }
     return Status.PERMISSION_DENIED.withDescription(
-        "Client " + altsContext.getPeerServiceAccount() + " is not authorized");
+        "Client " + peerServiceAccount + " is not authorized");
   }
 }

alts/src/test/java/io/grpc/alts/AuthorizationUtilTest.java

@@ -55,6 +55,14 @@ public void altsAuthorizationCheck() throws Exception {
     assertThat(status.getDescription()).endsWith("not authorized");
   }
 
+  @Test
+  public void altsAuthorizationCheck_ignoresCase() throws Exception {
+    Status status =
+        AuthorizationUtil.clientAuthorizationCheck(
+            new FakeServerCall("alice"), Lists.newArrayList("ALICE", "Bob"));
+    assertThat(status.getCode()).isEqualTo(Status.Code.OK);
+  }
+
   private static class FakeServerCall extends ServerCall<String, String> {
     final Attributes attrs;