auth: Use pre-existing private key in test

Generating a KeyPair is very expensive when running with TSAN, because
TSAN keeps the JVM in interpreted mode. This speeds up the test running
on my desktop from .368s to .151s; faster, but nobody cares. With TSAN,
the speedup is from 150-500s to 4-6s. Within Google the test was timing
out because it was taking so long. While we can increase the timeout,
it seems better to speed up the test in this easy way.

Author: ejona86

auth/src/test/java/io/grpc/auth/GoogleAuthLibraryCallCredentialsTest.java

@@ -50,10 +50,12 @@
 import io.grpc.Status;
 import io.grpc.internal.JsonParser;
 import io.grpc.testing.TestMethodDescriptors;
+import io.grpc.testing.TlsTesting;
+import io.grpc.util.CertificateUtils;
 import java.io.IOException;
+import java.io.InputStream;
 import java.net.URI;
-import java.security.KeyPair;
-import java.security.KeyPairGenerator;
+import java.security.PrivateKey;
 import java.util.ArrayList;
 import java.util.Date;
 import java.util.List;
@@ -342,15 +344,18 @@ public void serviceUri() throws Exception {
 
   @Test
   public void serviceAccountToJwt() throws Exception {
-    KeyPair pair = KeyPairGenerator.getInstance("RSA").generateKeyPair();
+    PrivateKey privateKey;
+    try (InputStream server1Key = TlsTesting.loadCert("server1.key")) {
+      privateKey = CertificateUtils.getPrivateKey(server1Key);
+    }
 
     HttpTransportFactory factory = Mockito.mock(HttpTransportFactory.class);
     Mockito.when(factory.create()).thenThrow(new AssertionError());
 
     ServiceAccountCredentials credentials =
         ServiceAccountCredentials.newBuilder()
             .setClientEmail("[email protected]")
-            .setPrivateKey(pair.getPrivate())
+            .setPrivateKey(privateKey)
             .setPrivateKeyId("test-private-key-id")
             .setHttpTransportFactory(factory)
             .build();
@@ -390,13 +395,16 @@ public void oauthClassesNotInClassPath() throws Exception {
 
   @Test
   public void jwtAccessCredentialsInRequestMetadata() throws Exception {
-    KeyPair pair = KeyPairGenerator.getInstance("RSA").generateKeyPair();
+    PrivateKey privateKey;
+    try (InputStream server1Key = TlsTesting.loadCert("server1.key")) {
+      privateKey = CertificateUtils.getPrivateKey(server1Key);
+    }
 
     ServiceAccountCredentials credentials =
         ServiceAccountCredentials.newBuilder()
             .setClientId("test-client")
             .setClientEmail("[email protected]")
-            .setPrivateKey(pair.getPrivate())
+            .setPrivateKey(privateKey)
             .setPrivateKeyId("test-private-key-id")
             .setQuotaProjectId("test-quota-project-id")
             .build();