OpenIdConnect flow does not set the SignInAsAuthenticationType cookie

[Praburaj]

Checkin : 3483842#commitcomment-9535319 seems to break openIdconnect flow as it does not set the external cookie.

Test failure here : aspnet/MusicStore@7783c36 is due to this.

[kevinchalet]

On a side note, OpenIdConnectAuthenticationMiddleware doesn't use a correct value for TokenValidationParameters.AuthenticationType: it should use Options.AuthenticationType instead of externalOptions.Options.SignInAsAuthenticationType to make sure that the ClaimsIdentity returned by AuthenticateCoreAsync has the same AuthenticationType as the middleware itself.

https://github.com/aspnet/Security/blob/dev/src/Microsoft.AspNet.Security.OpenIdConnect/OpenIdConnectAuthenticationMiddleware.cs#L51

[Praburaj]

@brentschmaltz