Support non JWT tokens in OAuth flows

[rido-min]

There are some OAuth Providers in ABS, like GitHub, that do not produce JWT tokens, and seems the code in this repo assume all tokens are JWT.

[ERROR] Samples.Graph.Microsoft.Teams.Plugins.AspNetCore Microsoft.IdentityModel.Tokens.SecurityTokenMalformedException: IDX12709: CanReadToken() returned false. JWT is not well formed.
[ERROR] Samples.Graph.Microsoft.Teams.Plugins.AspNetCore The token needs to be in JWS or JWE Compact Serialization Format. (JWS): 'EncodedHeader.EncodedPayload.EncodedSignature'. (JWE): 'EncodedProtectedHeader.EncodedEncryptedKey.EncodedInitializationVector.EncodedCiphertext.EncodedAuthenticationTag'.
[ERROR] Samples.Graph.Microsoft.Teams.Plugins.AspNetCore    at System.IdentityModel.Tokens.Jwt.JwtSecurityTokenHandler.ReadJwtToken(String token)
[ERROR] Samples.Graph.Microsoft.Teams.Plugins.AspNetCore    at Microsoft.Teams.Api.Auth.JsonWebToken..ctor(Response response) in C:\_code\teams.net\Libraries\Microsoft.Teams.Api\Auth\JsonWebToken.cs:line 89
[ERROR] Samples.Graph.Microsoft.Teams.Plugins.AspNetCore    at Microsoft.Teams.Apps.App.OnVerifyStateActivity(IContext`1 context) in C:\_code\teams.net\Libraries\Microsoft.Teams.Apps\AppRouting.cs:line 147
[ERROR] Samples.Graph.Microsoft.Teams.Plugins.AspNetCore    at Microsoft.Teams.Apps.Routing.Route.Invoke(IContext`1 context) in C:\_code\teams.net\Libraries\Microsoft.Teams.Apps\Routing\Route.cs:line 30
[ERROR] Samples.Graph.Microsoft.Teams.Plugins.AspNetCore    at Microsoft.Teams.Apps.App.<>c__DisplayClass55_0.<<Process>g__Next|0>d.MoveNext() in C:\_code\teams.net\Libraries\Microsoft.Teams.Apps\App.cs:line 331
[ERROR] Samples.Graph.Microsoft.Teams.Plugins.AspNetCore --- End of stack trace from previous location ---
[ERROR] Samples.Graph.Microsoft.Teams.Plugins.AspNetCore    at Microsoft.Teams.Apps.App.Process(ISenderPlugin sender, ActivityEvent event, CancellationToken cancellationToken) in C:\_code\teams.net\Libraries\Microsoft.Teams.Apps\App.cs:line 391
[ERROR] Samples.Graph.Microsoft.Teams.Plugins.AspNetCore    at Microsoft.Teams.Apps.Events.EventEmitter.<>c__DisplayClass7_0`1.<<On>b__0>d.MoveNext() in C:\_code\teams.net\Libraries\Microsoft.Teams.Apps\Events\EventEmitter.cs:line 69
[ERROR] Samples.Graph.Microsoft.Teams.Plugins.AspNetCore --- End of stack trace from previous location ---
[ERROR] Samples.Graph.Microsoft.Teams.Plugins.AspNetCore    at Microsoft.Teams.Apps.Events.Topic.Emit(IPlugin plugin, Event event, CancellationToken cancellationToken) in C:\_code\teams.net\Libraries\Microsoft.Teams.Apps\Events\Topic.cs:line 17
[ERROR] Samples.Graph.Microsoft.Teams.Plugins.AspNetCore    at Microsoft.Teams.Apps.Events.EventEmitter.Emit(IPlugin plugin, String name, Event event, CancellationToken cancellationToken) in C:\_code\teams.net\Libraries\Microsoft.Teams.Apps\Events\EventEmitter.cs:line 83
[ERROR] Samples.Graph.Microsoft.Teams.Plugins.AspNetCore    at Microsoft.Teams.Apps.App.<>c__DisplayClass68_0.<<AddPlugin>b__0>d.MoveNext() in C:\_code\teams.net\Libraries\Microsoft.Teams.Apps\AppPlugins.cs:line 44
[ERROR] Samples.Graph.Microsoft.Teams.Plugins.AspNetCore --- End of stack trace from previous location ---
[ERROR] Samples.Graph.Microsoft.Teams.Plugins.AspNetCore    at Microsoft.Teams.Plugins.AspNetCore.AspNetCorePlugin.Do(ActivityEvent event, CancellationToken cancellationToken) in C:\_code\teams.net\Libraries\Microsoft.Teams.Plugins\Microsoft.Teams.Plugins.AspNetCore\AspNetCorePlugin.cs:line 149
[ERROR] Samples.Graph Microsoft.IdentityModel.Tokens.SecurityTokenMalformedException: IDX12709: CanReadToken() returned false. JWT is not well formed.
[ERROR] Samples.Graph The token needs to be in JWS or JWE Compact Serialization Format. (JWS): 'EncodedHeader.EncodedPayload.EncodedSignature'. (JWE): 'EncodedProtectedHeader.EncodedEncryptedKey.EncodedInitializationVector.EncodedCiphertext.EncodedAuthenticationTag'.
[ERROR] Samples.Graph    at System.IdentityModel.Tokens.Jwt.JwtSecurityTokenHandler.ReadJwtToken(String token)
[ERROR] Samples.Graph    at Microsoft.Teams.Api.Auth.JsonWebToken..ctor(Response response) in C:\_code\teams.net\Libraries\Microsoft.Teams.Api\Auth\JsonWebToken.cs:line 89
[ERROR] Samples.Graph    at Microsoft.Teams.Apps.App.OnVerifyStateActivity(IContext`1 context) in C:\_code\teams.net\Libraries\Microsoft.Teams.Apps\AppRouting.cs:line 147
[ERROR] Samples.Graph    at Microsoft.Teams.Apps.Routing.Route.Invoke(IContext`1 context) in C:\_code\teams.net\Libraries\Microsoft.Teams.Apps\Routing\Route.cs:line 30
[ERROR] Samples.Graph    at Microsoft.Teams.Apps.App.<>c__DisplayClass55_0.<<Process>g__Next|0>d.MoveNext() in C:\_code\teams.net\Libraries\Microsoft.Teams.Apps\App.cs:line 331
[ERROR] Samples.Graph --- End of stack trace from previous location ---
[ERROR] Samples.Graph    at Microsoft.Teams.Apps.App.Process(ISenderPlugin sender, ActivityEvent event, CancellationToken cancellationToken) in C:\_code\teams.net\Libraries\Microsoft.Teams.Apps\App.cs:line 391
[ERROR] Samples.Graph    at Microsoft.Teams.Apps.Events.EventEmitter.<>c__DisplayClass7_0`1.<<On>b__0>d.MoveNext() in C:\_code\teams.net\Libraries\Microsoft.Teams.Apps\Events\EventEmitter.cs:line 69
[ERROR] Samples.Graph --- End of stack trace from previous location ---
[ERROR] Samples.Graph    at Microsoft.Teams.Apps.Events.Topic.Emit(IPlugin plugin, Event event, CancellationToken cancellationToken) in C:\_code\teams.net\Libraries\Microsoft.Teams.Apps\Events\Topic.cs:line 17
[ERROR] Samples.Graph    at Microsoft.Teams.Apps.Events.EventEmitter.Emit(IPlugin plugin, String name, Event event, CancellationToken cancellationToken) in C:\_code\teams.net\Libraries\Microsoft.Teams.Apps\Events\EventEmitter.cs:line 83
[ERROR] Samples.Graph    at Microsoft.Teams.Apps.App.<>c__DisplayClass68_0.<<AddPlugin>b__0>d.MoveNext() in C:\_code\teams.net\Libraries\Microsoft.Teams.Apps\AppPlugins.cs:line 44
[ERROR] Samples.Graph --- End of stack trace from previous location ---
[ERROR] Samples.Graph    at Microsoft.Teams.Plugins.AspNetCore.AspNetCorePlugin.Do(ActivityEvent event, CancellationToken cancellationToken) in C:\_code\teams.net\Libraries\Microsoft.Teams.Plugins\Microsoft.Teams.Plugins.AspNetCore\AspNetCorePlugin.cs:line 149
[DEBUG] Samples.Graph.Microsoft.Teams.Plugins.AspNetCore.DevTools OnError
[INFO] Microsoft.AspNetCore.Http.Result.JsonResult Setting HTTP status code 500.