Redirect Uri coming from unknown source

Hi there,

I am using .net to redirect users to the login page. The code for doing that looks like this:

[ApiController]
[Route(“api/[controller]”)]
public class AccountController : ControllerBase
{

[EnableCors(“InternalCalls”)]
[HttpGet(“Login”, Name = “Login”)]
public async Task Login(string returnUrl = “https://.net/select”)
{
var authenticationProperties = new LoginAuthenticationPropertiesBuilder()
.WithRedirectUri(returnUrl)
.Build();
await HttpContext.ChallengeAsync(Auth0Constants.AuthenticationScheme, authenticationProperties);

}
}

Now for some reason, when I hit up the URL to login, it says “Callback URL mismatch.
The provided redirect_uri is not in the list of allowed callback URLs.”

I checked the logs and the redirect_uri is shown as https://.net/callback instead of aforementioned https://.net/select. I have no idea where this uri is coming from. The code is clearly calling the redirect_uri with the return URL.

Where is this uri coming from?