Add Signing.singer_email (#89)
diff --git a/google/auth/credentials.py b/google/auth/credentials.py
index 470f1a4..360dc0e 100644
--- a/google/auth/credentials.py
+++ b/google/auth/credentials.py
@@ -229,3 +229,10 @@
# pylint: disable=missing-raises-doc,redundant-returns-doc
# (pylint doesn't recognize that this is abstract)
raise NotImplementedError('Sign bytes must be implemented.')
+
+ @abc.abstractproperty
+ def signer_email(self):
+ """Optional[str]: An email address that identifies the signer."""
+ # pylint: disable=missing-raises-doc
+ # (pylint doesn't recognize that this is abstract)
+ raise NotImplementedError('Signer email must be implemented.')