Register - 2023 App Security

[Route("api/[controller]")]
[ApiController]
public class AuthenticationController : ControllerBase
{
    private readonly UserManager<AppUser> _userManager;
    private readonly IRepository _repository;
    private readonly IUserClaimsPrincipalFactory<AppUser> _claimsPrincipalFactory;
    private readonly IConfiguration _configuration;

    public AuthenticationController(UserManager<AppUser> userManager, IUserClaimsPrincipalFactory<AppUser> claimsPrincipalFactory, IConfiguration configuration, IRepository repository)
    {
        _userManager = userManager;
        _claimsPrincipalFactory = claimsPrincipalFactory;
        _configuration = configuration;
        _repository = repository;
    }

    [HttpPost]
    [Route("RegisterUser")]
    public async Task<IActionResult>RegisterUser(UserViewModel uvm)
    {
        var user = await _userManager.FindByNameAsync(uvm.username);
        if (user == null)
        {
            try
            {
                string phoneNumberPattern = @"^0\d{9}$";
                bool isValidPhoneNumber = Regex.IsMatch(uvm.phonenumber, phoneNumberPattern);
                if (!isValidPhoneNumber) return BadRequest("Please enter a valid 10-digit phone number");
                user = new AppUser
                {
                    Id= Guid.NewGuid().ToString(),
                    UserName= uvm.username,
                    Email=  uvm.emailaddress,
                    PhoneNumber= uvm.phonenumber
                };
                var result= await _userManager.CreateAsync(user, uvm.password);
                if (result.Errors.Count() > 0)
                {
                    StringBuilder errorlist = new StringBuilder("These registration errors need to be resolved");
                    foreach (var error in result.Errors)
                    {
                        errorlist.Append($"{error.Code}: {error.Description}");
                    }
                    return BadRequest($"{errorlist}");
                }
            }
            catch (Exception ex)
            {
                return StatusCode(StatusCodes.Status500InternalServerError, $"Error occured{ex.Message}");
            }
        }
        else
        {
            return Conflict($"The username '{uvm.username}' already exists. Please use a different username");
        }
        return Ok($"Your account '{uvm.username}' was created successfully. You may proceed with logging in");
    }
}