title: Using ASP.NET identity to do external oauth logins, how can add parameters to the facebook authorization endpoint? I want to pass "display=popup"
body: <p>I'm using ASP.NET MVC 6 (.net core).  With it, i'm using the built in external login logic in order to authenticate with facebook. </p>
  
  <p>I've made a modification to it so that instead of authenticating within the same window, i'm launching a popup and authenticating there. Once successful, the popup closes itself and tells my main window to redirect.  This all works.</p>
  
  <p>However, I want to use the "smaller/mini" version of the facebook login page.  This can be seen here:
  <a href="https://www.facebook.com/login.php?display=popup" rel="nofollow">https://www.facebook.com/login.php?display=popup</a></p>
  
  <p>"display=popup" is what is controlling it.</p>
  
  <p>I don't see how i can inject this kvp in my C# code. Where can i do it?</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
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  <pre class="snippet-code-js lang-js prettyprint-override"><code>app.UseFacebookAuthentication(new FacebookOptions
                                {
                          // was hoping for something here... tried to stick it into the authorizationurl but then i end up with 2 question marks and it fails
                                AppId = "blah",
                                AppSecret = "blah"
                                });</code></pre>
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  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-js lang-js prettyprint-override"><code>        [AllowAnonymous]
          public IActionResult ExternalLogin(string provider, string returnUrl = null)
          {
              var redirectUrl = Url.Action("ExternalLoginCallback", "Account", new { ReturnUrl = returnUrl });
              var properties = _signInManager.ConfigureExternalAuthenticationProperties(provider, redirectUrl);
  
            // Don't see anything here... 
            
              return Challenge(properties, provider);
          }</code></pre>
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