Make Distinction Between "p" and "r" Paths Clearer

[9p4]

Is your feature request related to a problem? Please describe.
It seems like there isn't enough of a distinction between the p and r paths for initialization and redirection respectively. Perhaps make the different clearer?

Describe the solution you'd like
Replace the p paths with start and r with redirect.

Describe alternatives you've considered
Improve the documentation perhaps?

Additional context
#49
#82
#55
#106

[9p4]

Whatever solution is created, it should NOT break existing configs. p and r paths should still work, but the documentation should all point to the new paths.

[esmondmissen]

How do we want to handle the redirect url changing. Making the routes have multiple paths is easy but the redirect url needs to be configured on the authentication side.

When we get to the code below we have no way of telling if they have configured their redirect url to /r/ or /redirect/. Could we assume that if they use /start/ we will use /redirect/ and if they use /p/ we will use /r/?

var options = new OidcClientOptions
            {
                Authority = config.OidEndpoint?.Trim(),
                ClientId = config.OidClientId?.Trim(),
                ClientSecret = config.OidSecret?.Trim(),
                RedirectUri = GetRequestBase() + "/sso/OID/r/" + provider,
                Scope = string.Join(" ", config.OidScopes.Prepend("openid profile")),
            };

[esmondmissen]

Something like this:

RedirectUri = GetRequestBase() + $"/sso/OID/{(Request.Path.Value.Contains("/start/", StringComparison.InvariantCultureIgnoreCase) ? "redirect" : "r")}/" + provider,

[9p4]

I guess there isn't any other option if the auth provider has a whitelist of URLs to redirect to

[9p4]

Fixed in defab9c