private (IAppUser user, string provider, string providerUserId, IEnumerable <Claim> claims) FindUserFromExternalProvider(AuthenticateResult result)
{
var externalUser = result.Principal;
// 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 = externalUser.FindFirst(JwtClaimTypes.Subject) ??
externalUser.FindFirst(ClaimTypes.NameIdentifier) ??
throw new Exception("Unknown userid");
// remove the user id claim so we don't include it as an extra claim if/when we provision the user
var claims = externalUser.Claims.ToList();
claims.Remove(userIdClaim);
var provider = result.Properties.Items["scheme"];
var providerUserId = userIdClaim.Value;
// find external user
var user = _users.FindByExternalProvider(provider, providerUserId);
return(user, provider, providerUserId, claims);
}
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;
// 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
//
// (This is not necessary adding to your LDAP, in this case we keep it in memory or in Redis as a reference.
// I don't think it's a good idea to update your own Ldap for this except maybe for some scenario.
var user = _userStore.FindByExternalProvider(provider, userId);
if (user == default(IAppUser))
{
// this sample simply auto-provisions new external user
// another common approach is to start a registrations workflow first
user = _userStore.AutoProvisionUser(provider, userId, claims);
}
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
var returnUrl = result.Properties.Items["returnUrl"];
if (_interaction.IsValidReturnUrl(returnUrl) || Url.IsLocalUrl(returnUrl))
{
return(Redirect(returnUrl));
}
return(Redirect("~/"));
}