C# – How override ASP.NET Core Identity’s password policy

By default, ASP.NET Core Identity's password policy require at least one special character, one uppercase letter, one number, …

How can I change this restrictions ?

There is nothing about that in the documentation (https://docs.asp.net/en/latest/security/authentication/identity.html)

I try to override the Identity's User Manager but I don't see which method manages the password policy.

public class ApplicationUserManager : UserManager<ApplicationUser>
{
    public ApplicationUserManager(
        DbContextOptions<SecurityDbContext> options,
        IServiceProvider services,
        IHttpContextAccessor contextAccessor,
        ILogger<UserManager<ApplicationUser>> logger)
        : base(
              new UserStore<ApplicationUser>(new SecurityDbContext(contextAccessor)),
              new CustomOptions(),
              new PasswordHasher<ApplicationUser>(),
              new UserValidator<ApplicationUser>[] { new UserValidator<ApplicationUser>() },
              new PasswordValidator[] { new PasswordValidator() },
              new UpperInvariantLookupNormalizer(),
              new IdentityErrorDescriber(),
              services,
              logger
            // , contextAccessor
              )
    {
    }

    public class PasswordValidator : IPasswordValidator<ApplicationUser>
    {
        public Task<IdentityResult> ValidateAsync(UserManager<ApplicationUser> manager, ApplicationUser user, string password)
        {
            return Task.Run(() =>
            {
                if (password.Length >= 4) return IdentityResult.Success;
                else { return IdentityResult.Failed(new IdentityError { Code = "SHORTPASSWORD", Description = "Password too short" }); }
            });
        }
    }

    public class CustomOptions : IOptions<IdentityOptions>
    {
        public IdentityOptions Value { get; private set; }
        public CustomOptions()
        {
            Value = new IdentityOptions
            {
                ClaimsIdentity = new ClaimsIdentityOptions(),
                Cookies = new IdentityCookieOptions(),
                Lockout = new LockoutOptions(),
                Password = null,
                User = new UserOptions(),
                SignIn = new SignInOptions(),
                Tokens = new TokenOptions()
            };
        }
    }
}

I add this user manager dependency in startup's class :

services.AddScoped<ApplicationUserManager>();

But when I'm using ApplicationUserManager in controllers, I have the error :
An unhandled exception occurred while processing the request.

InvalidOperationException: Unable to resolve service for type 'Microsoft.EntityFrameworkCore.DbContextOptions`1[SecurityDbContext]' while attempting to activate 'ApplicationUserManager'.

EDIT: User's management works when I use the ASP.NET Core Identity's default classes, so it's not a database problem, or something like this

EDIT 2 : I found the solution, you have just to configure Identity in the startup's class. My answer gives some details.