Owin authentication remove special caracters

Question

I have owin authentication on application .Net 4.7.2 Once form is submitted, in network is see special caracters but it's lost once it's entenred in method GrantResourceOwnerCredentials

Do you have any idea how to configure this to allow special caracters ? Thanks

Startup.cs

public class Startup
{      
    // ConfigureAuth method  
    public static void ConfigureAuth(IAppBuilder app)
    {
        app.UseCors(CorsOptions.AllowAll);

        OAuthAuthorizationServerOptions option = new OAuthAuthorizationServerOptions
        {
            TokenEndpointPath = new PathString("/token"),
            Provider = new ApplicationOAuthProvider(),
            AccessTokenExpireTimeSpan = TimeSpan.FromMinutes(180),              
            AllowInsecureHttp = true,
    };
        app.UseOAuthAuthorizationServer(option);
        app.UseOAuthBearerAuthentication(new OAuthBearerAuthenticationOptions());
    }


    public void Configuration(IAppBuilder app)
    {
        ConfigureAuth(app);
        // Pour plus d'informations sur la configuration de votre application, visitez https://go.microsoft.com/fwlink/?LinkID=316888
    }


}

and

  public class ApplicationOAuthProvider : OAuthAuthorizationServerProvider
{
    public override async Task ValidateClientAuthentication(OAuthValidateClientAuthenticationContext context)
    {
        context.Validated();
    }

    public override async Task GrantResourceOwnerCredentials(OAuthGrantResourceOwnerCredentialsContext context)
    {
        try
        {
            var userStore = new UserStore<ApplicationUser>(new ApplicationDbContext());
            var manager = new UserManager<ApplicationUser>(userStore);
            var user = await manager.FindAsync(context.UserName, context.Password);
            if (user != null)
            {
                var identity = new ClaimsIdentity(context.Options.AuthenticationType);
                identity.AddClaim(new Claim("Username", user.UserName));
                identity.AddClaim(new Claim("Email", user.Email));
                identity.AddClaim(new Claim("FirstName", user.FirstName ?? ""));
                identity.AddClaim(new Claim("LastName", user.LastName ?? user.UserName));
                identity.AddClaim(new Claim("LoggedOn", DateTime.Now.ToString()));
                context.Validated(identity);
            }
            else
                return;
        }
        catch (Exception ex)
        {

         throw;
        }
    }
}