Change CredentialsProvider::TokenListener to use StatusOr<Token> (#945)

* Change CredentialsProvider::TokenListener to use StatusOr

Rather than a token plus error code/msg.

* Eliminate the concept of an invalid Token

Instead, we'll just use StatusOr<Token>. Note that unauthenticated
tokens are handled as a special case; they're created via:
  Token::Unauthenticated()
and are otherwise "valid", though attempting to retrieve the raw token
on one of these tokens will cause an assertion failure.

1 files changed, 5 insertions, 7 deletions

diff --git a/Firestore/core/src/firebase/firestore/auth/token.cc b/Firestore/core/src/firebase/firestore/auth/token.cc
index 4ee1b69..6fe5fc4 100644
--- a/Firestore/core/src/firebase/firestore/auth/token.cc
+++ b/Firestore/core/src/firebase/firestore/auth/token.cc
@@ -21,15 +21,13 @@ namespace firestore {
 namespace auth {
 
 Token::Token(const absl::string_view token, const User& user)
-    : token_(token), user_(user), is_valid_(true) {
+    : token_(token), user_(user) {
 }
 
-Token::Token() : token_(), user_(User::Unauthenticated()), is_valid_(false) {
-}
-
-const Token& Token::Invalid() {
-  static const Token kInvalidToken;
-  return kInvalidToken;
+const Token& Token::Unauthenticated() {
+  static const Token kUnauthenticatedToken(absl::string_view(),
+                                           User::Unauthenticated());
+  return kUnauthenticatedToken;
 }
 
 }  // namespace auth