Fixes error handling in firebase_auth on Android and iOS

[slightfoot]

This standardises the error responses from the platform implementations. All functions in FirebaseAuth and FirebaseUser are now documented with error codes.

Fixes: flutter/flutter#18312 and Fixes: flutter/flutter#20223

This PR is based on #678 so includes the changes there.

Example:

PlatformException(ERROR_USER_NOT_FOUND, There is no user record corresponding to this identifier. The user may have been deleted., null)
PlatformException(ERROR_WRONG_PASSWORD, The password is invalid or the user does not have a password., null)
PlatformException(ERROR_NETWORK_REQUEST_FAILED, Network error (such as timeout, interrupted connection or unreachable host) has occurred., null)

Other changes include:

• Added missing linkWithTwitterCredential method.
• Updated deprecated API fetchProvidersForEmail to fetchSignInMethodsForEmail.
• Added unlinkCredential.
• Updated Changelog.

Full error code list can be found here:
https://docs.google.com/spreadsheets/d/1FDn0rRRYjgXMwc_FIAxO7_cQh69q5VXgQt7Hmvyb1Sg/edit?usp=sharing

Closes: #768 and Closes: #697 - Merged into this one.
Closes: #703 and #814

[slightfoot]

@kroikie this is now ready for review and merge.

[slightfoot]

Another big change in this code is that now all the dart code of firebase_auth is now documented.

@kroikie I just noticed my PR overlaps several others noted here. I just fixed things as I saw they were missing when adding the error logging.

• [firebase_auth] Adding support for FirebaseUser.unlink(providerId) #703 is included as unlinkCredential on the platform interface and unlinkEmailAndPassword/unlinkGoogleCredential/unlinkFacebookCredential/unlinkTwitterCredential on the FirebaseUser object. This matches the style of API we have in dart for signIn and link.
• adding support auth link for Twitter #697 this is now defunct, all functionality is in this PR and has been documented also.
• Support sign-in with Github and linking Github accounts to existing users #768 overlaps with adding support auth link for Twitter #697 as it provides Twitter and Github login. I can merge this PR into this one and provide Github login feature with documentation if you like.

Would be nice to see #718 merged in the same version release as this.

[filleduchaos]

@slightfoot I don't mind you taking the changes from #768! :)

[escamoteur]

@eseidelGoogle could you check on this please? It's really a needed fix.

[eseidelGoogle]

@bparrishMines may also be able to help with reviews.

[bparrishMines]

HI @slightfoot,

Thanks for your contribution! Could you resolve the recent conflicts? I'll finish reviewing it as soon as you do.

[slightfoot]

@bparrishMines think the analyze queue broken. Its been waiting a few hours. I'll double check all the formatting is good tomorrow when the results come in. Other than that, this is ready to go.

[slightfoot]

@kroikie looks like the build server is borked. perhaps you can kick it. 😉

[bparrishMines]

Most of it looks great! I only have a few small comments. I'll see what I can do about the analyzer.

[bparrishMines]

Why do you not use exception.getMessage() for this and the other exceptions below?

[slightfoot]

Changed.

[bparrishMines]

An extra space after documentation is unnecessary if we go by effective dart style guide. Same for comments below.

[slightfoot]

Thanks, changed these also.

[bparrishMines]

Since there is only deprecation, you don't have to put **Breaking Change**

[slightfoot]

Updated.

[bparrishMines]

cc @fkorotkov @gspencergoog Do you know why the analyze check is stuck here?

[HerrNiklasRaab]

When will this change be released?

[beardo01]

I support getting this merged too. Let's get it done please.

[kroikie]

@slightfoot Sorry about the delay on this PR. Would you be able to rebase this on master then I'd be happy to merge.

[manhnhhdvn]

@bparrishMines , @kroikie

This PR is wonderful, but if it seems time consuming, could you review #703 and #814 first?

#703 is the unlink part of this PR.
#814 is the fetchSignInMethodsForEmail part of this PR.

[slightfoot]

@bparrishMines @kroikie It's ready to merge.

[kroikie]

@slightfoot sorry for the churn here, could you rebase then should be good to merge.

[slightfoot]

Rebased.

[slightfoot]

@kroikie I've rebased again, and merged whilst I can, but leave the release to you.

[xqwzts]

@slightfoot Thanks for the long-awaited and hugely useful commit.

An official release would be appreciated as this fixes some critical bugs wrt error handling.

Renaming fetchProvidersForEmail to fetchSignInMethodsForEmail is a breaking change though, surely it warrants a mention in the changelog and a version bump?

[slightfoot]

@xqwzts I was asked to remove my "breaking change" mention from the CHANGELOG and the @deprecated function I had because we have not yet reached stable API version, or something.

[HerrNiklasRaab]

How is the status? When will this be in beta?

[ghost]

@slightfoot Do you know when this will be available?

[georgeherby]

If you want these changes before an official release but without the stuff in the proposed 0.7.0 in the change log
just add this to your yaml

  firebase_auth:
    git:
      url: git://github.com/flutter/plugins.git
      ref: e96fb0c350328ff77baae758b6dc70797117ac98
      path: packages/firebase_auth

The commit is of the stuff in this PR which in the changelog is 0.6.7 - just get the most recent commit if you want the stuff in 0.7.0 but that is nothing to do with this PR

[slightfoot]

@kroikie is it possible to push this out. A lot of people are still waiting for this. 0.6.7 never got released. we are still on 0.6.6.

[baeharam]

Complete?

[sumitrvi]

Hey i'm also facing google signin issue in ios
Unhandled Exception: PlatformException(ERROR_INTERNAL_ERROR, An internal error has occurred, print and inspect the error details for more information., null)
#0 StandardMethodCodec.decodeEnvelope (package:flutter/src/services/message_codecs.dart:569:7)
#1 MethodChannel.invokeMethod (package:flutter/src/services/platform_channel.dart:321:33)

#2 MethodChannel.invokeMapMethod (package:flutter/src/services/platform_channel.dart:349:48)
#3 MethodChannelFirebaseAuth.signInWithCredential (package:firebase_auth_platform_interface/src/method_channel_firebase_auth.dart:161:23)
#4 FirebaseAuth.signInWithCredential (package:firebase_auth/src/firebase_auth.dart:208:10)
#5 _AsyncAwaitCompleter.start (dart:async-patch/async_patch.dart:45:6)
#6 FirebaseAuth.signInWithCredential (package:firebase_auth/src/firebase_auth.dart:205:42)
#7 _SigninScreenState.socialLogin (package:down_beatflutterproject/screens/signinscreen.<…>