Managed subtransport: support Default Credentials

Author: ethomson

LibGit2Sharp/Core/ManagedHttpSmartSubtransport.cs

@@ -199,8 +199,16 @@ private HttpResponseMessage GetResponseWithRedirects()
                                 throw new InvalidOperationException("authentication cancelled");
                             }
 
-                            UsernamePasswordCredentials userpass = (UsernamePasswordCredentials)cred;
-                            credentials = new NetworkCredential(userpass.Username, userpass.Password);
+                            if (cred is DefaultCredentials)
+                            {
+                                credentials = CredentialCache.DefaultNetworkCredentials;
+                            }
+                            else if (cred is UsernamePasswordCredentials)
+                            {
+                                UsernamePasswordCredentials userpass = (UsernamePasswordCredentials)cred;
+                                credentials = new NetworkCredential(userpass.Username, userpass.Password);
+                            }
+
                             continue;
                         }
                         else if (response.StatusCode == HttpStatusCode.Moved || response.StatusCode == HttpStatusCode.Redirect)

LibGit2Sharp/SmartSubtransport.cs

@@ -106,6 +106,10 @@ public int AcquireCredentials(out Credentials cred, string user, params Type[] m
                 {
                     allowed |= (int)GitCredentialType.UserPassPlaintext;
                 }
+                else if (method == typeof(DefaultCredentials))
+                {
+                    allowed |= (int)GitCredentialType.Default;
+                }
                 else
                 {
                     throw new InvalidOperationException("Unknown type passes as allowed credential");
@@ -133,6 +137,9 @@ public int AcquireCredentials(out Credentials cred, string user, params Type[] m
                     case GitCredentialType.UserPassPlaintext:
                         cred = UsernamePasswordCredentials.FromNative((GitCredentialUserpass*) credHandle);
                         return 0;
+                    case GitCredentialType.Default:
+                        cred = new DefaultCredentials();
+                        return 0;
                     default:
                         throw new InvalidOperationException("User returned an unkown credential type");
                 }