github: support gist remote URLs for GitHub

We have not been consistently detecting or normalising "gist" URLs for
dotcom or GHES instances.

Gists are backed by a Git repository and can be cloned/pushed-to etc
like a normal repository. Credentials are the same as the base site.

Update our OAuth, rest API, and dotcom-detection methods that deal with
the remote or target URL to correctly support gists URLs. Also add some
tests around this.

src/shared/GitHub.Tests/GitHubHostProviderTests.cs

@@ -15,8 +15,11 @@ public class GitHubHostProviderTests
         [InlineData("https://github.com", true)]
         [InlineData("https://gitHUB.CoM", true)]
         [InlineData("https://GITHUB.COM", true)]
+        [InlineData("https://gist.github.com", true)]
         [InlineData("https://foogithub.com", false)]
         [InlineData("https://api.github.com", false)]
+        [InlineData("https://api.gist.github.com", false)]
+        [InlineData("https://foogist.github.com", false)]
         public void GitHubHostProvider_IsGitHubDotCom(string input, bool expected)
         {
             Assert.Equal(expected, GitHubHostProvider.IsGitHubDotCom(new Uri(input)));
@@ -98,6 +101,8 @@ public void GitHubHostProvider_GetCredentialServiceUrl(string protocol, string h
         [InlineData("https://GitHub.Com", "none", GitHubConstants.DotComAuthenticationModes)]
         [InlineData("https://github.com", null, GitHubConstants.DotComAuthenticationModes)]
         [InlineData("https://GitHub.Com", null, GitHubConstants.DotComAuthenticationModes)]
+        [InlineData("https://gist.github.com", null, GitHubConstants.DotComAuthenticationModes)]
+        [InlineData("https://GIST.GITHUB.COM", null, GitHubConstants.DotComAuthenticationModes)]
         public async Task GitHubHostProvider_GetSupportedAuthenticationModes(string uriString, string gitHubAuthModes, AuthenticationModes expectedModes)
         {
             var targetUri = new Uri(uriString);

src/shared/GitHub.Tests/GitHubRestApiTests.cs

@@ -2,8 +2,6 @@
 using System.Linq;
 using System.Net;
 using System.Net.Http;
-using System.Net.Http.Headers;
-using System.Text;
 using System.Threading.Tasks;
 using GitCredentialManager.Tests;
 using GitCredentialManager.Tests.Objects;
@@ -13,6 +11,20 @@ namespace GitHub.Tests
 {
     public class GitHubRestApiTests
     {
+        [Theory]
+        [InlineData("https://github.com", "user", "https://api.github.com/user")]
+        [InlineData("https://github.com", "users/123", "https://api.github.com/users/123")]
+        [InlineData("https://gItHuB.cOm", "uSeRs/123", "https://api.github.com/uSeRs/123")]
+        [InlineData("https://gist.github.com", "user", "https://api.github.com/user")]
+        [InlineData("https://github.example.com", "user", "https://github.example.com/api/v3/user")]
+        [InlineData("https://raw.github.example.com", "user", "https://github.example.com/api/v3/user")]
+        [InlineData("https://gist.github.example.com", "user", "https://github.example.com/api/v3/user")]
+        public void GitHubRestApi_GetApiRequestUri(string targetUrl, string apiUrl, string expected)
+        {
+            Uri actualUri = GitHubRestApi.GetApiRequestUri(new Uri(targetUrl), apiUrl);
+            Assert.Equal(expected, actualUri.ToString());
+        }
+
         [Fact]
         public async Task GitHubRestApi_AcquireTokenAsync_NullUri_ThrowsException()
         {

src/shared/GitHub/GitHubHostProvider.cs

@@ -487,10 +487,12 @@ public static bool IsGitHubDotCom(Uri targetUri)
         {
             EnsureArgument.AbsoluteUri(targetUri, nameof(targetUri));
 
-            return StringComparer.OrdinalIgnoreCase.Equals(targetUri.Host, GitHubConstants.GitHubBaseUrlHost);
+            // github.com or gist.github.com are both considered dotcom
+            return StringComparer.OrdinalIgnoreCase.Equals(targetUri.Host, GitHubConstants.GitHubBaseUrlHost) ||
+                   StringComparer.OrdinalIgnoreCase.Equals(targetUri.Host, GitHubConstants.GistBaseUrlHost);
         }
 
-        private static Uri NormalizeUri(Uri uri)
+        internal static Uri NormalizeUri(Uri uri)
         {
             if (uri is null)
             {
@@ -500,8 +502,9 @@ private static Uri NormalizeUri(Uri uri)
             // Special case for gist.github.com which are git backed repositories under the hood.
             // Credentials for these repositories are the same as the one stored with "github.com".
             // Same for gist.github[.subdomain].domain.tld. The general form was already checked via IsSupported.
-            int firstDot = uri.DnsSafeHost.IndexOf(".");
-            if (firstDot > -1 && uri.DnsSafeHost.Substring(0, firstDot).Equals("gist", StringComparison.OrdinalIgnoreCase)) {
+            int firstDot = uri.DnsSafeHost.IndexOf(".", StringComparison.Ordinal);
+            if (firstDot > -1 && uri.DnsSafeHost.Substring(0, firstDot).Equals("gist", StringComparison.OrdinalIgnoreCase))
+            {
                 return new Uri("https://" + uri.DnsSafeHost.Substring(firstDot+1));
             }
 

src/shared/GitHub/GitHubOAuth2Client.cs

@@ -11,8 +11,11 @@ public GitHubOAuth2Client(HttpClient httpClient, ISettings settings, Uri baseUri
             : base(httpClient, CreateEndpoints(baseUri),
                 GetClientId(settings), trace2, GetRedirectUri(settings, baseUri), GetClientSecret(settings)) { }
 
-        private static OAuth2ServerEndpoints CreateEndpoints(Uri baseUri)
+        private static OAuth2ServerEndpoints CreateEndpoints(Uri uri)
         {
+            // Ensure that the base URI is normalized to support Gist subdomains
+            Uri baseUri = GitHubHostProvider.NormalizeUri(uri);
+
             Uri authEndpoint = new Uri(baseUri, GitHubConstants.OAuthAuthorizationEndpointRelativeUri);
             Uri tokenEndpoint = new Uri(baseUri, GitHubConstants.OAuthTokenEndpointRelativeUri);
             Uri deviceAuthEndpoint = new Uri(baseUri, GitHubConstants.OAuthDeviceEndpointRelativeUri);

src/shared/GitHub/GitHubRestApi.cs

@@ -203,7 +203,7 @@ private async Task<AuthenticationResult> ParseSuccessResponseAsync(Uri targetUri
             }
         }
 
-        private Uri GetApiRequestUri(Uri targetUri, string apiUrl)
+        internal /* for testing */ static Uri GetApiRequestUri(Uri targetUri, string apiUrl)
         {
             if (GitHubHostProvider.IsGitHubDotCom(targetUri))
             {
@@ -214,8 +214,13 @@ private Uri GetApiRequestUri(Uri targetUri, string apiUrl)
                 // If we're here, it's GitHub Enterprise via a configured authority
                 var baseUrl = targetUri.GetLeftPart(UriPartial.Authority);
 
+                RegexOptions reOptions = RegexOptions.CultureInvariant | RegexOptions.IgnoreCase;
+
                 // Check for 'raw.' in the hostname and remove it to get the correct GHE API URL
-                baseUrl = Regex.Replace(baseUrl, @"^(https?://)raw\.", "$1", RegexOptions.CultureInvariant | RegexOptions.IgnoreCase);
+                baseUrl = Regex.Replace(baseUrl, @"^(https?://)raw\.", "$1", reOptions);
+
+                // Likewise check for `gist.` in the hostname and remove it to get the correct GHE API URL
+                baseUrl = Regex.Replace(baseUrl, @"^(https?://)gist\.", "$1", reOptions);
 
                 return new Uri(baseUrl + $"/api/v3/{apiUrl}");
             }