added comments

Author: daniel-sanche

google/auth/crypt/_cryptography_rsa.py

@@ -62,6 +62,10 @@ def _warn_rsa_type(key_type):
 class RSAVerifier(base.Verifier):
     """Verifies RSA cryptographic signatures using public keys.
 
+    Note: rsa.key.PublicKey keys are currently supported, but the `rsa` library
+    is deprecated. Please migrate to `cryptography` keys or use
+    `.from_string()` instead
+
     Args:
         public_key (
                 cryptography.hazmat.primitives.asymmetric.rsa.RSAPublicKey):
@@ -117,6 +121,10 @@ def from_string(cls, public_key):
 class RSASigner(base.Signer, base.FromServiceAccountMixin):
     """Signs messages with an RSA private key.
 
+    Note: rsa.key.PrivateKey keys are currently supported, but the `rsa` library
+    is deprecated. Please migrate to `cryptography` keys or use
+    `.from_string()` instead
+
     Args:
         private_key (
                 cryptography.hazmat.primitives.asymmetric.rsa.RSAPrivateKey):

tests/crypt/test__cryptography_rsa.py

@@ -179,6 +179,9 @@ def test_pickle(self):
 
 @pytest.mark.skipif(rsa is None, reason="rsa library is not installed")
 class TestRSATransparency(object):
+    """
+    RSASigner and RSAVerifier should be backwards compatible with rsa keys
+    """
     @classmethod
     def setup_class(cls):
         import rsa