s2a: inject Optional<AccessTokenManager> in tests

Author: rmehta19

s2a/src/main/java/io/grpc/s2a/internal/handshaker/GetAuthenticationMechanisms.java

@@ -24,19 +24,21 @@
 /** Retrieves the authentication mechanism for a given local identity. */
 @Immutable
 final class GetAuthenticationMechanisms {
-  private static final Optional<AccessTokenManager> TOKEN_MANAGER = AccessTokenManager.create();
+  static final Optional<AccessTokenManager> TOKEN_MANAGER = AccessTokenManager.create();
 
   /**
    * Retrieves the authentication mechanism for a given local identity.
    *
    * @param localIdentity the identity for which to fetch a token.
+   * @param tokenManager the token manager to use for fetching tokens.
    * @return an {@link AuthenticationMechanism} for the given local identity.
    */
-  static Optional<AuthenticationMechanism> getAuthMechanism(Optional<S2AIdentity> localIdentity) {
-    if (!TOKEN_MANAGER.isPresent()) {
+  static Optional<AuthenticationMechanism> getAuthMechanism(Optional<S2AIdentity> localIdentity,
+      Optional<AccessTokenManager> tokenManager) {
+    if (!tokenManager.isPresent()) {
       return Optional.empty();
     }
-    AccessTokenManager manager = TOKEN_MANAGER.get();
+    AccessTokenManager manager = tokenManager.get();
     // If no identity is provided, fetch the default access token and DO NOT attach an identity
     // to the request.
     if (!localIdentity.isPresent()) {

s2a/src/main/java/io/grpc/s2a/internal/handshaker/SslContextFactory.java

@@ -105,7 +105,8 @@ private static GetTlsConfigurationResp.ClientTlsConfiguration getClientTlsConfig
       reqBuilder.setLocalIdentity(localIdentity.get().getIdentity());
     }
     Optional<AuthenticationMechanism> authMechanism =
-        GetAuthenticationMechanisms.getAuthMechanism(localIdentity);
+        GetAuthenticationMechanisms.getAuthMechanism(localIdentity,
+        GetAuthenticationMechanisms.TOKEN_MANAGER);
     if (authMechanism.isPresent()) {
       reqBuilder.addAuthenticationMechanisms(authMechanism.get());
     }

s2a/src/test/java/io/grpc/s2a/internal/handshaker/GetAuthenticationMechanismsTest.java

@@ -18,9 +18,11 @@
 
 import com.google.common.truth.Expect;
 import io.grpc.s2a.internal.handshaker.S2AIdentity;
+import io.grpc.s2a.internal.handshaker.tokenmanager.AccessTokenManager;
 import io.grpc.s2a.internal.handshaker.tokenmanager.SingleTokenFetcher;
 import java.util.Optional;
 import org.junit.AfterClass;
+import org.junit.Before;
 import org.junit.BeforeClass;
 import org.junit.Rule;
 import org.junit.Test;
@@ -33,6 +35,7 @@ public final class GetAuthenticationMechanismsTest {
   @Rule public final Expect expect = Expect.create();
   private static final String TOKEN = "access_token";
   private static String originalAccessToken;
+  private Optional<AccessTokenManager> tokenManager;
 
   @BeforeClass
   public static void setUpClass() {
@@ -41,6 +44,11 @@ public static void setUpClass() {
     SingleTokenFetcher.setAccessToken(TOKEN);
   }
 
+  @Before
+  public void setUp() {
+    tokenManager = AccessTokenManager.create();
+  }
+
   @AfterClass
   public static void tearDownClass() {
     SingleTokenFetcher.setAccessToken(originalAccessToken);
@@ -49,7 +57,7 @@ public static void tearDownClass() {
   @Test
   public void getAuthMechanisms_emptyIdentity_success() {
     expect
-        .that(GetAuthenticationMechanisms.getAuthMechanism(Optional.empty()))
+        .that(GetAuthenticationMechanisms.getAuthMechanism(Optional.empty(), tokenManager))
         .isEqualTo(
             Optional.of(AuthenticationMechanism.newBuilder().setToken("access_token").build()));
   }
@@ -58,7 +66,7 @@ public void getAuthMechanisms_emptyIdentity_success() {
   public void getAuthMechanisms_nonEmptyIdentity_success() {
     S2AIdentity fakeIdentity = S2AIdentity.fromSpiffeId("fake-spiffe-id");
     expect
-        .that(GetAuthenticationMechanisms.getAuthMechanism(Optional.of(fakeIdentity)))
+        .that(GetAuthenticationMechanisms.getAuthMechanism(Optional.of(fakeIdentity), tokenManager))
         .isEqualTo(
             Optional.of(
                 AuthenticationMechanism.newBuilder()