How to change Identity error for register page in razor pages

I have a basic question. I want to customize errors that IdentityResult add to ModelState. this is my code(the foreach in else add errors):

var user = new IdentityUser {UserName = Input.Phone, PhoneNumber = Input.Phone};    
var result = await _userManager.CreateAsync(user, Input.Password);
                if (result.Succeeded)
                {
                    //Do something...
                }
                else
                {
                    foreach (var error in result.Errors)
                    {
                        //how can I change error.Description?
                        ModelState.AddModelError(string.Empty, error.Description);
                    }
                }

Answer

You can override methods of IdentityErrorDescriber to change identity error messages.

public class YourIdentityErrorDescriber : IdentityErrorDescriber
{
    public override IdentityError DuplicateUserName(string username)
    {
        return new IdentityError
        {
            Code = nameof(DuplicateUserName),
            Description = "This is a error"
        };
       //other method in IdentityErrorDescriber,you can see below
    }
}

Then you can register it in startup(.AddErrorDescriber<YourIdentityErrorDescriber>();).

services.AddDefaultIdentity<IdentityUser>(options => options.SignIn.RequireConfirmedAccount = false)
            .AddEntityFrameworkStores<ApplicationDbContext>().AddErrorDescriber<YourIdentityErrorDescriber>();

About the method in IdentityErrorDescriber.

public class CustomIdentityErrorDescriber : IdentityErrorDescriber
{
    public override IdentityError DefaultError() { return new IdentityError { Code = nameof(DefaultError), Description = $"An unknown failure has occurred." }; }
    public override IdentityError ConcurrencyFailure() { return new IdentityError { Code = nameof(ConcurrencyFailure), Description = "Optimistic concurrency failure, object has been modified." }; }
    public override IdentityError PasswordMismatch() { return new IdentityError { Code = nameof(PasswordMismatch), Description = "Incorrect password." }; }
    public override IdentityError InvalidToken() { return new IdentityError { Code = nameof(InvalidToken), Description = "Invalid token." }; }
    public override IdentityError LoginAlreadyAssociated() { return new IdentityError { Code = nameof(LoginAlreadyAssociated), Description = "A user with this login already exists." }; }
    public override IdentityError InvalidUserName(string userName) { return new IdentityError { Code = nameof(InvalidUserName), Description = $"User name '{userName}' is invalid, can only contain letters or digits." }; }
    public override IdentityError InvalidEmail(string email) { return new IdentityError { Code = nameof(InvalidEmail), Description = $"Email '{email}' is invalid."  }; }
    public override IdentityError DuplicateUserName(string userName) { return new IdentityError { Code = nameof(DuplicateUserName), Description = $"User Name '{userName}' is already taken."  }; }
    public override IdentityError DuplicateEmail(string email) { return new IdentityError { Code = nameof(DuplicateEmail), Description = $"Email '{email}' is already taken."  }; }
    public override IdentityError InvalidRoleName(string role) { return new IdentityError { Code = nameof(InvalidRoleName), Description = $"Role name '{role}' is invalid."  }; }
    public override IdentityError DuplicateRoleName(string role) { return new IdentityError { Code = nameof(DuplicateRoleName), Description = $"Role name '{role}' is already taken."  }; }
    public override IdentityError UserAlreadyHasPassword() { return new IdentityError { Code = nameof(UserAlreadyHasPassword), Description = "User already has a password set." }; }
    public override IdentityError UserLockoutNotEnabled() { return new IdentityError { Code = nameof(UserLockoutNotEnabled), Description = "Lockout is not enabled for this user." }; }
    public override IdentityError UserAlreadyInRole(string role) { return new IdentityError { Code = nameof(UserAlreadyInRole), Description = $"User already in role '{role}'."  }; }
    public override IdentityError UserNotInRole(string role) { return new IdentityError { Code = nameof(UserNotInRole), Description = $"User is not in role '{role}'."  }; }
    public override IdentityError PasswordTooShort(int length) { return new IdentityError { Code = nameof(PasswordTooShort), Description = $"Passwords must be at least {length} characters."  }; }
    public override IdentityError PasswordRequiresNonAlphanumeric() { return new IdentityError { Code = nameof(PasswordRequiresNonAlphanumeric), Description = "Passwords must have at least one non alphanumeric character." }; }
    public override IdentityError PasswordRequiresDigit() { return new IdentityError { Code = nameof(PasswordRequiresDigit), Description = "Passwords must have at least one digit ('0'-'9')." }; }
    public override IdentityError PasswordRequiresLower() { return new IdentityError { Code = nameof(PasswordRequiresLower), Description = "Passwords must have at least one lowercase ('a'-'z')." }; }
    public override IdentityError PasswordRequiresUpper() { return new IdentityError { Code = nameof(PasswordRequiresUpper), Description = "Passwords must have at least one uppercase ('A'-'Z')." }; }
}

Test result:

enter image description here

Refer to this answer.