How to customize ASP.NET Identity Core Username to allow special characters and space

Question

I have changed my Register Action Method to accept user Name instead of Email.

if (ModelState.IsValid)
{
    var user = new ApplicationUser          


        

Answer 1

The proposed solution can be tricky if you have an exhaustive list of special characters to whitelist.

If you want to blacklist instead, disable the whitelist in startup.cs:

 services.AddIdentity(
                options =>
                {                        
                    options.User.AllowedUserNameCharacters = string.Empty;
                })

Then create your custom user validator

 public class UsernameValidator : IUserValidator
where TUser : User
{
    public Task ValidateAsync(UserManager manager, TUser user)
    {                
        if (user.UserName.Any(x=>x ==':' || x == ';' || x == ' ' || x == ','))
        {
            return Task.FromResult(IdentityResult.Failed(new IdentityError
            {
                Code = "InvalidCharactersUsername",
                Description = "Username can not contain ':', ';', ' ' or ','"
            }));
        }
        return Task.FromResult(IdentityResult.Success);
    }        
}

Then add it to startup.cs:

 services.AddIdentity(
                options =>
                {
                    options.Password = new PasswordOptions
                    {
                        RequiredLength = 8,
                        RequireUppercase = true,
                        RequireNonAlphanumeric = true,
                        RequireDigit = true,
                        RequireLowercase = true
                    };
                    options.User.AllowedUserNameCharacters = string.Empty;
                }).AddUserValidator>()