Retrieving email from Facebook Login in ASP.NET MVC throwing null exception - asp.net

Question

I am developing an ASP.NET MVC application. In my application, I need to provide Faccebook Login service to user. Besides, I need retrieve the user email from Facebook and store in the database.
I am using Visual Studio 2013 and ASP.NET MVC5. My Facebook login method is working fine. But when I retrieve email from Facebook, it is giving me null exception. My externalLoginCallback method is below:
[AllowAnonymous]
public async Task<ActionResult> ExternalLoginCallback(string returnUrl)
{
var result = await AuthenticationManager.AuthenticateAsync(DefaultAuthenticationTypes.ExternalCookie);
if (result == null || result.Identity == null)
{
return RedirectToAction("Login");
}
var idClaim = result.Identity.FindFirst(ClaimTypes.NameIdentifier);
if (idClaim == null)
{
return RedirectToAction("Login");
}
var login = new UserLoginInfo(idClaim.Issuer, idClaim.Value);
var name = result.Identity.Name == null ? "" : result.Identity.Name.Replace(" ", "");
//retrieving email from facebook here
var externalIdentity = HttpContext.GetOwinContext().Authentication.GetExternalIdentityAsync(DefaultAuthenticationTypes.ExternalCookie);
var emailClaim = externalIdentity.Result.Claims.FirstOrDefault(c => c.Type == ClaimTypes.Email);
var email = emailClaim.Value;//this line is throwing null exception
.
.
.
}
I commented where error throw in my code.
This is how I configured Facebook in Startup.Auth.cs
var facebookAuthenticationOptions = new FacebookAuthenticationOptions()
{
AppId = "x",
AppSecret = "y"
};
facebookAuthenticationOptions.Scope.Add("email");
app.UseFacebookAuthentication(facebookAuthenticationOptions);
I also tried like this:
app.UseFacebookAuthentication(new FacebookAuthenticationOptions
{
AppId = "x",
AppSecret = "y",
Scope = { "email" },
Provider = new FacebookAuthenticationProvider
{
OnAuthenticated = context =>
{
context.Identity.AddClaim(new System.Security.Claims.Claim("FacebookAccessToken", context.AccessToken));
return Task.FromResult(true);
}
}
});
Both are not working. What is wrong with my code and how can I fix it?

Answer 1

You can try this:
var facebookAuthenticationOptions = new FacebookAuthenticationOptions()
{
AppId = "xxxxxxx",
AppSecret = "xxxxxx",
BackchannelHttpHandler = new FacebookBackChannelHandler(),
UserInformationEndpoint = "https://graph.facebook.com/v2.4/me?fields=id,name,email,first_name,last_name,location"
};
and then define this class:
public class FacebookBackChannelHandler : HttpClientHandler
{
protected override async System.Threading.Tasks.Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, System.Threading.CancellationToken cancellationToken)
{
if (!request.RequestUri.AbsolutePath.Contains("/oauth"))
{
request.RequestUri = new Uri(request.RequestUri.AbsoluteUri.Replace("?access_token", "&access_token"));
}
var response = await base.SendAsync(request, cancellationToken);
return response;
}
}
finally, you can get email (and first_name,last_name,location) by doing the following in "ExternalLoginCallback" method in account controller:
[AllowAnonymous]
public async Task<ActionResult> ExternalLoginCallback(string returnUrl)
{
var loginInfo = await AuthenticationManager.GetExternalLoginInfoAsync();
if (loginInfo == null)
{
return RedirectToAction("LoginRegister");
}
// GET MAIL AND NAME
var email = loginInfo.ExternalIdentity.Claims.FirstOrDefault(c => c.Type == ClaimTypes.Email).Value;
var name= loginInfo.ExternalIdentity.Claims.FirstOrDefault(c => c.Type == ClaimTypes.Name).Value;