I working on a .NET Core 3.1 project using Identity. On the Login.cs.html page, the OnGetAsync() page handler is as follows:
public async Task OnGetAsync(string returnUrl = null)
{
if (!string.IsNullOrEmpty(ErrorMessage))
{
ModelState.AddModelError(string.Empty, ErrorMessage);
}
returnUrl = returnUrl ?? Url.Content("~/");
// Clear the existing external cookie to ensure a clean login process
await HttpContext.SignOutAsync(IdentityConstants.ExternalScheme);
ExternalLogins = (await _signInManager.GetExternalAuthenticationSchemesAsync())
.ToList();
ReturnUrl = returnUrl;
}
I'm a bit confused about the line of code returnUrl = returnUrl ?? Url.Content("~/"); and why it is written this way. Why is it checking if returnUrl is null, won't it always be null? Why not remove the string returnUrl = null as a method parameter and assign ReturnUrl = Url.Content("~/");? Am I missing some thing here?
The returnUrl parameter has been set up to use an optional argument:
If no argument is sent for that parameter, the default value is used.
With the default setup for Identity, the value for returnUrl comes from the query-string of the request URL. For example, the following URL provides a value for the returnUrl argument:
/Identity/Account/Login?returnUrl=/Some/Protected/Route
In this case, returnUrl will not be null. However, consider the following URL:
/Identity/Account/Login
In this case, returnUrl will be null. There's no URL to redirect to after the login process completes, so the line you've called out will set it to Url.Content("~/"). That just means it'll end up redirecting the user to the root of the web application, which is typically the home page.
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