fix: use enum for possible algorithms

Author: diegomarquezp

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

@@ -228,13 +228,14 @@ static GdchCredentials fromJson(Map<String, Object> json, HttpTransportFactory t
   /**
    * Internal constructor.
    *
-   * @param privateKeyPkcs8 RSA private key object for the service account in PKCS#8 format.
+   * @param privateKeyPkcs8 EC private key object for the service account in PKCS#8 format.
    * @param builder A builder for GdchCredentials.
    * @return an instance of GdchCredentials.
    */
   static GdchCredentials fromPkcs8(String privateKeyPkcs8, GdchCredentials.Builder builder)
       throws IOException {
-    PrivateKey privateKey = OAuth2Utils.privateKeyFromPkcs8(privateKeyPkcs8, "EC");
+    PrivateKey privateKey =
+        OAuth2Utils.privateKeyFromPkcs8(privateKeyPkcs8, OAuth2Utils.Pkcs8Algorithm.EC);
     builder.setPrivateKey(privateKey);
 
     return new GdchCredentials(builder);

oauth2_http/java/com/google/auth/oauth2/OAuth2Utils.java

@@ -79,6 +79,11 @@
  */
 public class OAuth2Utils {
 
+  public enum Pkcs8Algorithm {
+    RSA,
+    EC
+  }
+
   static final String SIGNATURE_ALGORITHM = "SHA256withRSA";
 
   public static final String TOKEN_TYPE_ACCESS_TOKEN =
@@ -266,7 +271,7 @@ static Map<String, Object> validateMap(Map<String, Object> map, String key, Stri
    *     key creation.
    */
   public static PrivateKey privateKeyFromPkcs8(String privateKeyPkcs8) throws IOException {
-    return privateKeyFromPkcs8(privateKeyPkcs8, "RSA");
+    return privateKeyFromPkcs8(privateKeyPkcs8, Pkcs8Algorithm.RSA);
   }
 
   /**
@@ -278,7 +283,7 @@ public static PrivateKey privateKeyFromPkcs8(String privateKeyPkcs8) throws IOEx
    * @throws IOException if the PKCS#8 data is invalid or if an unexpected exception occurs during
    *     key creation.
    */
-  public static PrivateKey privateKeyFromPkcs8(String privateKeyPkcs8, String algorithm)
+  public static PrivateKey privateKeyFromPkcs8(String privateKeyPkcs8, Pkcs8Algorithm algorithm)
       throws IOException {
     Reader reader = new StringReader(privateKeyPkcs8);
     Section section = PemReader.readFirstSectionAndClose(reader, "PRIVATE KEY");
@@ -289,7 +294,7 @@ public static PrivateKey privateKeyFromPkcs8(String privateKeyPkcs8, String algo
     PKCS8EncodedKeySpec keySpec = new PKCS8EncodedKeySpec(bytes);
     Exception unexpectedException;
     try {
-      KeyFactory keyFactory = KeyFactory.getInstance(algorithm);
+      KeyFactory keyFactory = KeyFactory.getInstance(algorithm.toString());
       return keyFactory.generatePrivate(keySpec);
     } catch (NoSuchAlgorithmException | InvalidKeySpecException exception) {
       unexpectedException = exception;

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

@@ -1208,7 +1208,8 @@ void signUsingEsSha256_producesVerifiableSignature() throws Exception {
 
   @Test
   void signUsingEsSha256_validStructure() throws Exception {
-    PrivateKey privateKey = OAuth2Utils.privateKeyFromPkcs8(PRIVATE_KEY_PKCS8, "EC");
+    PrivateKey privateKey =
+        OAuth2Utils.privateKeyFromPkcs8(PRIVATE_KEY_PKCS8, OAuth2Utils.Pkcs8Algorithm.EC);
     JsonFactory jsonFactory = GsonFactory.getDefaultInstance();
 
     JsonWebSignature.Header header = new JsonWebSignature.Header();