CODE EXAMPLE FOR CSHARP

c# allowedusernamecharacters

services.AddIdentity<ApplicationUser, IdentityRole>(options => {
    options.User.AllowedUserNameCharacters = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789-._@+/ ";
});