Unable to generate token by using OAuth - asp.net-web-api

Question

Firstly I want to tell those who are going to mark this question as copied or existing that I have seen the solution exist but neither one help me in my case.
I am using my custom model which is going to register the users and at the time of generating token the credential user entered is going to match the record in my custom model if the user exist it return the token and if not it return the exception .
This is my custom model class.
public class userregistration
{
public int ID { get; set; }
[Required]
public string UserName { get; set; }
[Required]
[DataType(DataType.EmailAddress)]
public string Email { get; set; }
[Required]
[DataType(DataType.Password)]
public string Password { get; set; }
[Required]
[DataType(DataType.Password)]
[Display(Name = "Confirm password")]
[Compare("Password", ErrorMessage = "The password and confirmation password do not match.")]
public string ConfirmPassword { get; set; }
}
This is my OAuthAuthrizationServerProvider
public class MyAutorization : OAuthAuthorizationServerProvider
{
public override Task ValidateClientAuthentication(OAuthValidateClientAuthenticationContext context)
{
context.Validated();
return Task.FromResult(0);
}
public override async Task GrantResourceOwnerCredentials(OAuthGrantResourceOwnerCredentialsContext context)
{
context.OwinContext.Response.Headers.Add("Access-Control-Allow-Origin", new[] { "*" });
using (RegistrationRepos repo = new RegistrationRepos())
{
userregistration user = await repo.FindUser(context.UserName, context.Password);
if (user == null)
{
context.SetError("invalid_grant", "The user name or password is incorrect.");
return;
}
}
var identity = new ClaimsIdentity(context.Options.AuthenticationType);
identity.AddClaim(new Claim("sub", context.UserName));
identity.AddClaim(new Claim("role", "user"));
In the above section I am calling FindUser method from my RegistrationRepos which is going to return the user by comparing the credential with existing record.
The RegistrationRepos Class is here
public class RegistrationRepos : IDisposable
{
private MyContext context = new MyContext();
protected DbSet<userregistration> DbSet { get; set; }
public RegistrationRepos()
{
DbSet = context.Set<userregistration>();
}
public async Task<userregistration> FindUser(string userName, string password)
{
var user = await DbSet.FirstOrDefaultAsync(x => x.UserName == userName && x.Password == password);
return user;
}
public void Dispose()
{
context.Dispose();
}
}
This is all working fine when i debug the solution the user is returning fine if the credential matches and it is returning Null if the credential does not match , But instead of generating the token it is returning {"error":"invalid_grant"}
MY Owing Startup class is here.
public class owinstartup
{
public void Configuration(IAppBuilder app)
{
// For more information on how to configure your application, visit http://go.microsoft.com/fwlink/?LinkID=316888
app.UseCors(Microsoft.Owin.Cors.CorsOptions.AllowAll); // enables cors origin request
var myProvider = new MyAutorization();
OAuthAuthorizationServerOptions options = new OAuthAuthorizationServerOptions
{
AllowInsecureHttp = true,
TokenEndpointPath = new PathString("/token"),
AccessTokenExpireTimeSpan = TimeSpan.FromHours(1),
Provider = myProvider
};
app.UseOAuthAuthorizationServer(options);
app.UseOAuthBearerAuthentication(new OAuthBearerAuthenticationOptions());
HttpConfiguration config = new HttpConfiguration();
WebApiConfig.Register(config);
}
}
What is the issue behind the scene?