LoginController.cs

using FirebaseAdmin.Auth;

[Route("login")]
public class LoginController : ControllerBase
{
    private readonly UserStore userStore = new UserStore();

    [HttpPost]
    public async Task<ActionResult> Login([FromBody] LoginRequest request)
    {
        try
        {
            var user = await this.userStore.LoginAsync(request);
            var token = await FirebaseAuth.DefaultInstance.CreateCustomTokenAsync(
                user.Uid, user.Claims);
            return this.Ok(new LoginResult()
            {
                CustomToken = token,
            });
        }
        catch (Exception e)
        {
            return this.StatusCode(401, new { Error = e.Message });
        }
    }
}