unusual function definition - what is happening here

Question

I was going through the identity server 4 doc and I came across this piece of code.

private (TestUser 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);
}

and it is called like this.

var (user, provider, providerUserId, claims) = FindUserFromExternalProvider(result);

I dont quiet understand what is happening here. what sort of function definition usage is this?

Answer 1

You mean the returned data? It's a value tuple that is returned, see this article for a guide to Value Tuples. Value Tuples is a way to return multiple parameters without creating a custom class.

The method tries to lookup the user in the local database after the user has externally authenticated.