[flutter_appauth] feat: web support

[eirikb]

Add web support with PKCE auth.
Only supports redirect! No popup (yet).

Ok, so I've been using flutter_appauth for a while, with great success. For web support I have implemented my own solution. Now I started yet another Flutter project where I add flutter_appauth (for mobile) and start copying over my auth solution (for web), but, this time I figured I could try to add the solution directly into flutter_appauth.

I'm aware of #70 and honestly don't know if this PR will solve that.
It only works with redirect, and the "Sign in with auto code exchange" is the only button in example that will work.

[SamC-Apadmi]

Any movement on this? It'd be really useful for me in the near future. I'm happy to jump in and help resolve the conflicts if that'd be useful?

[eirikb]

Ah didn't know I've got conflicts. Thanks for the heads up @SamC-Apadmi I'll fix that right away.
FWIW we have been running my fork now since I made it.
It seems to have a small issue that we have to click "login" again. I haven't looked at it and people are like "oh well that's how it is". Worth fixing perhaps before merge

[MaikuB]

Sorry, somehow missed this one.

I'm aware of #70 and honestly don't know if this PR will solve that.

No, this will not solve it. Whilst I have not looked at that thread in a very long time, I believe one of the key points raised back then and at least in the OP is how this plugin is a wrapper/bridge for AppAuth SDKs. It's part of the name of this plugin as a result and the name AppAuth carries a connotation of referring the SDKs mentioned at https://appauth.io/. Since the PR here doesn't rely on the SDKs then it does not meet the criteria of being a wrapper.

With that in mind, I'll be closing this and I'll also look to create a FAQ section around this.