public async Task <IActionResult> ExternalLoginCallback()
{
// read external identity from the temporary cookie
var result = await HttpContext.AuthenticateAsync(IdentityServer4.IdentityServerConstants.ExternalCookieAuthenticationScheme);
if (result?.Succeeded != true)
{
throw new Exception("External authentication error");
}
// retrieve claims of the external user
var externalUser = result.Principal;
var claims = externalUser.Claims.ToList();
// try to determine the unique id of the external user (issued by the provider)
// the most common claim type for that are the sub claim and the NameIdentifier
// depending on the external provider, some other claim type might be used
var userIdClaim = claims.FirstOrDefault(x => x.Type == JwtClaimTypes.Subject);
if (userIdClaim == null)
{
userIdClaim = claims.FirstOrDefault(x => x.Type == ClaimTypes.NameIdentifier);
}
if (userIdClaim == null)
{
throw new Exception("Unknown userid");
}
// remove the user id claim from the claims collection and move to the userId property
// also set the name of the external authentication provider
claims.Remove(userIdClaim);
var provider = result.Properties.Items["scheme"];
var userId = userIdClaim.Value;
var returnUrl = result.Properties.Items["returnUrl"];
// this is where custom logic would most likely be needed to match your users from the
// external provider's authentication result, and provision the user as you see fit.
//
// check if the external user is already provisioned
var user = _userRepository.GetUserByProvider(provider, userId);
if (user == null)
{
// User wasn't found by Provider, but maybe one exists with the same e-mail address
if (provider == "Facebook")
{
var email = claims.FirstOrDefault(c => c.Type == "http://schemas.xmlsoap.org/ws/2005/05/identity/claims/emailaddress" || c.Type == "http://schemas.xmlsoap.org/ws/2005/05/identity/claims/email");
if (email != null)
{
var userByEmail = _userRepository.GetUserByEmail(email.Value);
if (userByEmail != null)
{
// Add Facebook as a provider for this user
_userRepository.AddUserLogin(userByEmail.SubjectId, provider, userId);
if (!_userRepository.Save())
{
throw new Exception($"Adding a login for a user failed.");
}
// Redirect to ExternalLoginCallback
var continueWithUrlAfterAddingUserLogin =
Url.Action("ExternalLoginCallback", new { returnUrl = returnUrl });
return(Redirect(continueWithUrlAfterAddingUserLogin));
}
}
}
var returnUrlAfterRegistration = Url.Action("ExternalLoginCallback", new { returnUrl = returnUrl });
var continueWithUrl = Url.Action("RegisterUser", "UserRegistration"
, new { returnUrl = returnUrlAfterRegistration, provider = provider, providerUserId = userId });
return(Redirect(continueWithUrl));
}
var additionalClaims = new List <Claim>();
// if the external system sent a session id claim, copy it over
// so we can use it for single sign-out
var sid = claims.FirstOrDefault(x => x.Type == JwtClaimTypes.SessionId);
if (sid != null)
{
additionalClaims.Add(new Claim(JwtClaimTypes.SessionId, sid.Value));
}
// if the external provider issued an id_token, we'll keep it for signout
AuthenticationProperties props = null;
var id_token = result.Properties.GetTokenValue("id_token");
if (id_token != null)
{
props = new AuthenticationProperties();
props.StoreTokens(new[] { new AuthenticationToken {
Name = "id_token", Value = id_token
} });
}
// issue authentication cookie for user
await _events.RaiseAsync(new UserLoginSuccessEvent(provider, userId, user.SubjectId, user.Username));
await HttpContext.SignInAsync(user.SubjectId, user.Username, provider, props, additionalClaims.ToArray());
// delete temporary cookie used during external authentication
await HttpContext.SignOutAsync(IdentityServer4.IdentityServerConstants.ExternalCookieAuthenticationScheme);
// validate return URL and redirect back to authorization endpoint or a local page
if (_interaction.IsValidReturnUrl(returnUrl) || Url.IsLocalUrl(returnUrl))
{
return(Redirect(returnUrl));
}
return(Redirect("~/"));
}
