Added LinkedInAuthenticationOptions.Proxy host for web applications running behind a proxy. This allows the middleware to authenticate for the proxy request host instead of the application request host. (#213)

src/Owin.Security.Providers.LinkedIn/LinkedInAuthenticationHandler.cs

@@ -61,7 +61,7 @@ namespace Owin.Security.Providers.LinkedIn
                     return new AuthenticationTicket(null, properties);
                 }
 
-                var requestPrefix = Request.Scheme + "://" + Request.Host;
+                var requestPrefix = Request.Scheme + "://" + this.GetHostName();
                 var redirectUri = requestPrefix + Request.PathBase + Options.CallbackPath;
 
                 // Build up the body for the token request
@@ -173,7 +173,7 @@ namespace Owin.Security.Providers.LinkedIn
             var baseUri =
                 Request.Scheme +
                 Uri.SchemeDelimiter +
-                Request.Host +
+                this.GetHostName() +
                 Request.PathBase;
 
             var currentUri =
@@ -271,5 +271,15 @@ namespace Owin.Security.Providers.LinkedIn
 
             return context.IsRequestCompleted;
         }
+
+        /// <summary>
+        ///     Gets proxy host name from <see cref="LinkedInAuthenticationOptions"/> if it is set.
+        ///     If proxy host name is not set, gets application request host name.
+        /// </summary>
+        /// <returns>Host name.</returns>
+        private string GetHostName()
+        {
+            return string.IsNullOrWhiteSpace(Options.ProxyHost) ? Request.Host.ToString() : Options.ProxyHost;
+        }
     }
 }

src/Owin.Security.Providers.LinkedIn/LinkedInAuthenticationOptions.cs

@@ -43,6 +43,16 @@ namespace Owin.Security.Providers.LinkedIn
         /// </summary>
         public PathString CallbackPath { get; set; }
 
+        /// <summary>
+        ///     Gets or sets the middleware host name.
+        ///     The middleware processes the <see cref="CallbackPath"/> on this host name instead of the application's request host.
+        ///     If this is not set, the application's request host will be used.
+        /// </summary>
+        /// <remarks>
+        ///     Use this property when running behind a proxy.
+        /// </remarks>
+        public string ProxyHost { get; set; }
+
         /// <summary>
         ///     Get or sets the text that the user can display on a sign in user interface.
         /// </summary>