registry: add auto-detection via HTTP query

Add the ability to let host providers additionally inspect a HTTP
response message to determine and identify a supported service/endpoint.

If the simple enumeration of providers matching against the static
`InputArguments` does not produce a match (at each priority level), then
check against the lazily evaluated HEAD call to the remote URL.

Author: mjcheetham

src/shared/Atlassian.Bitbucket/BitbucketHostProvider.cs

@@ -3,6 +3,7 @@
 using System;
 using System.Collections.Generic;
 using System.Net;
+using System.Net.Http;
 using System.Threading.Tasks;
 using Microsoft.Git.CredentialManager;
 using Microsoft.Git.CredentialManager.Authentication.OAuth;
@@ -53,7 +54,17 @@ public bool IsSupported(InputArguments input)
             return (StringComparer.OrdinalIgnoreCase.Equals(input.Protocol, "http") ||
                     StringComparer.OrdinalIgnoreCase.Equals(input.Protocol, "https")) &&
                    hostName.EndsWith(BitbucketConstants.BitbucketBaseUrlHost, StringComparison.OrdinalIgnoreCase);
+        }
+
+        public bool IsSupported(HttpResponseMessage response)
+        {
+            if (response is null)
+            {
+                return false;
+            }
 
+            // TODO: identify Bitbucket on-prem instances from the HTTP response
+            return false;
         }
 
         public async Task<ICredential> GetCredentialAsync(InputArguments input)

src/shared/GitHub/GitHubHostProvider.cs

@@ -2,6 +2,7 @@
 // Licensed under the MIT license.
 using System;
 using System.Collections.Generic;
+using System.Net.Http;
 using System.Threading.Tasks;
 using Microsoft.Git.CredentialManager;
 using Microsoft.Git.CredentialManager.Authentication.OAuth;
@@ -90,6 +91,17 @@ public override bool IsSupported(InputArguments input)
             return false;
         }
 
+        public override bool IsSupported(HttpResponseMessage response)
+        {
+            if (response is null)
+            {
+                return false;
+            }
+
+            // Look for a known GitHub.com/GHES header
+            return response.Headers.Contains("X-GitHub-Request-Id");
+        }
+
         public override string GetServiceName(InputArguments input)
         {
             var baseUri = new Uri(base.GetServiceName(input));

src/shared/Microsoft.AzureRepos/AzureReposHostProvider.cs

@@ -3,6 +3,7 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
+using System.Net.Http;
 using System.Threading.Tasks;
 using Microsoft.Git.CredentialManager;
 using Microsoft.Git.CredentialManager.Authentication;
@@ -58,6 +59,12 @@ public bool IsSupported(InputArguments input)
                    UriHelpers.IsAzureDevOpsHost(hostName);
         }
 
+        public bool IsSupported(HttpResponseMessage response)
+        {
+            // Azure DevOps Server (TFS) is handled by the generic provider, which supports basic auth, and WIA detection.
+            return false;
+        }
+
         public async Task<ICredential> GetCredentialAsync(InputArguments input)
         {
             string service = GetServiceName(input);
@@ -83,7 +90,7 @@ public async Task<ICredential> GetCredentialAsync(InputArguments input)
             return credential;
         }
 
-        public virtual Task StoreCredentialAsync(InputArguments input)
+        public Task StoreCredentialAsync(InputArguments input)
         {
             string service = GetServiceName(input);
 

src/shared/Microsoft.Git.CredentialManager/HostProvider.cs

@@ -3,6 +3,7 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
+using System.Net.Http;
 using System.Threading.Tasks;
 
 namespace Microsoft.Git.CredentialManager
@@ -34,6 +35,13 @@ public interface IHostProvider : IDisposable
         /// <returns>True if the provider supports the Git credential request, false otherwise.</returns>
         bool IsSupported(InputArguments input);
 
+        /// <summary>
+        /// Determine if the <see cref="HttpResponseMessage"/> identifies a recognized Git hosting provider.
+        /// </summary>
+        /// <param name="response">Response message of an endpoint query.</param>
+        /// <returns>True if the provider supports the host provider at the endpoint, false otherwise.</returns>
+        bool IsSupported(HttpResponseMessage response);
+
         /// <summary>
         /// Get a credential for accessing the remote Git repository on this hosting service.
         /// </summary>
@@ -78,6 +86,11 @@ protected HostProvider(ICommandContext context)
 
         public abstract bool IsSupported(InputArguments input);
 
+        public virtual bool IsSupported(HttpResponseMessage response)
+        {
+            return false;
+        }
+
         /// <summary>
         /// Return a string that uniquely identifies the service that a credential should be stored against.
         /// </summary>

src/shared/Microsoft.Git.CredentialManager/HostProviderRegistry.cs

@@ -3,6 +3,7 @@
 using System;
 using System.Collections.Generic;
 using System.Linq;
+using System.Net.Http;
 using System.Threading.Tasks;
 
 namespace Microsoft.Git.CredentialManager
@@ -45,7 +46,7 @@ public interface IHostProviderRegistry : IDisposable
 
     /// <summary>
     /// Host provider registry where each provider is queried by priority order until the first
-    /// provider that supports the credential query is found.
+    /// provider that supports the credential query or matches the endpoint query is found.
     /// </summary>
     public class HostProviderRegistry : IHostProviderRegistry
     {
@@ -87,7 +88,7 @@ public void Register(IHostProvider hostProvider, HostProviderPriority priority)
             providers.Add(hostProvider);
         }
 
-        public Task<IHostProvider> GetProviderAsync(InputArguments input)
+        public async Task<IHostProvider> GetProviderAsync(InputArguments input)
         {
             IHostProvider provider;
 
@@ -111,7 +112,7 @@ public Task<IHostProvider> GetProviderAsync(InputArguments input)
                     }
                     else
                     {
-                        return Task.FromResult(provider);
+                        return provider;
                     }
                 }
             }
@@ -137,7 +138,7 @@ public Task<IHostProvider> GetProviderAsync(InputArguments input)
                     }
                     else
                     {
-                        return Task.FromResult(provider);
+                        return provider;
                     }
                 }
             }
@@ -147,35 +148,51 @@ public Task<IHostProvider> GetProviderAsync(InputArguments input)
             //
             _context.Trace.WriteLine("Performing auto-detection of host provider.");
 
-            IHostProvider MatchProvider(HostProviderPriority priority)
+            var uri = input.GetRemoteUri();
+            var queryResponse = new Lazy<Task<HttpResponseMessage>>(() =>
+            {
+                _context.Trace.WriteLine("Querying remote URL for host provider auto-detection.");
+                return HttpClient.HeadAsync(uri);
+            });
+
+            async Task<IHostProvider> MatchProviderAsync(HostProviderPriority priority)
             {
                 if (_hostProviders.TryGetValue(priority, out ICollection<IHostProvider> providers))
                 {
                     _context.Trace.WriteLine($"Checking against {providers.Count} host providers registered with priority '{priority}'.");
 
+                    // Try matching using the static Git input arguments first (cheap)
                     if (providers.TryGetFirst(x => x.IsSupported(input), out IHostProvider match))
                     {
                         return match;
                     }
-                }
 
-                return null;
-            }
+                    HttpResponseMessage response = await queryResponse.Value;
 
-            provider = MatchProvider(HostProviderPriority.High) ??
-                       MatchProvider(HostProviderPriority.Normal) ??
-                       MatchProvider(HostProviderPriority.Low);
+                    // Try matching using the HTTP response from a query to the remote URL (expensive)
+                    if (providers.TryGetFirst(x => x.IsSupported(response), out match))
+                    {
+                        return match;
+                    }
+                }
 
-            if (provider is null)
-            {
-                throw new Exception("No host provider available to service this request.");
+                return null;
             }
 
-            return Task.FromResult(provider);
+            // Match providers starting with the highest priority
+            return await MatchProviderAsync(HostProviderPriority.High) ??
+                   await MatchProviderAsync(HostProviderPriority.Normal) ??
+                   await MatchProviderAsync(HostProviderPriority.Low) ??
+                   throw new Exception("No host provider available to service this request.");
         }
 
+        private HttpClient _httpClient;
+        private HttpClient HttpClient => _httpClient ??= _context.HttpClientFactory.CreateClient();
+
         public void Dispose()
         {
+            _httpClient?.Dispose();
+
             // Dispose of all registered providers to give them a chance to clean up and release any resources
             foreach (IHostProvider provider in _hostProviders.Values)
             {