Fixes base64URL encoding (#1161)

* Fixes base64URL encoding

* Addresses comments

* Addresses comment

1 files changed, 11 insertions, 1 deletions

diff --git a/Firebase/Auth/Source/FIRUser.m b/Firebase/Auth/Source/FIRUser.m
index 8dc5739..ea48267 100644
--- a/Firebase/Auth/Source/FIRUser.m
+++ b/Firebase/Auth/Source/FIRUser.m
@@ -845,8 +845,18 @@ static void callInMainThreadWithAuthDataResultAndError(
 - (FIRAuthTokenResult *)parseIDToken:(NSString *)token error:(NSError **)error {
   *error = nil;
   NSArray *tokenStringArray = [token componentsSeparatedByString:@"."];
+
   // The token payload is always the second index of the array.
-  NSMutableString *tokenPayload = [[NSMutableString alloc] initWithString:tokenStringArray[1]];
+  NSString *idToken = tokenStringArray[1];
+
+  // Convert the base64URL encoded string to a base64 encoded string.
+  // Replace "_" with "/"
+  NSMutableString *tokenPayload =
+      [[idToken stringByReplacingOccurrencesOfString:@"_" withString:@"/"] mutableCopy];
+
+  // Replace "-" with "+"
+  tokenPayload =
+      [[tokenPayload stringByReplacingOccurrencesOfString:@"-" withString:@"+"] mutableCopy];
 
   // Pad the token payload with "=" signs if the payload's length is not a multiple of 4.
   while ((tokenPayload.length % 4) != 0) {