Check if a password is valid using ASP.NET Identity 2

You can simply use PasswordValidator to check for password validity and errors as shown below:

var passwordValidator = new PasswordValidator<IdentityUser>();
var result = await passwordValidator.ValidateAsync(_userManager, null, "your password here");

if (result.Succeeded)
{
    // Valid Password
}
else
{
    // Check the error messages in result.Errors
}

Above solution works for Asp.Net Core 2.2

You may be able to use the PasswordValidator.ValidateAsync() method to determine if a password meets the criteria defined in your UserManager :

var valid = (await UserManager.PasswordValidator.ValidateAsync("pass")).Succeeded;