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ASP.NET Core HTTP Error Responses Best Practice?

How do you return a bad request or an unauthorized response in ASP.NET while also being able to return a strongly typed response? I present to you ActionResult<T>. Here is an example of me using ActionResult to validate the request as well as to check authorization. Since this is an example, is it not for copy-pasting but rather to show you how to use ActionResult<T> in practice.

// one of these is imports may be relevant
using System.Security.Claims;
using Microsoft.AspNetCore.Authorization;
using Microsoft.AspNetCore.Mvc;

public async Task<ActionResult<string>> New(StartRideRequest startRideRequest) {
    var email = User.FindFirstValue(ClaimTypes.Email);
    if (email == null) return Unauthorized();
    if (!_dataValidationService.validCurrency(startRideRequest.Currency)) {
        HttpContext.Features.Set(new ArgumentException("invalid currency"));
        return BadRequest("invalid currency");
    // ...
    return Ok("id");