Issue-267 Add fingerprint header, to autodetect Bitbucket DC instances.

Copied and refreshed the Bitbucket development doc from the Git Credential Manager for Windows project.

docs/bitbucket-development.md

@@ -0,0 +1,80 @@
+# Bitbucket Authentication, 2FA and OAuth
+
+By default for authenticating against private Git repositories Bitbucket supports SSH and username/password Basic Auth over HTTPS.
+Username/password Basic Auth over HTTPS is also available for REST API access.
+Additionally Bitbucket supports App-specific passwords which can be used via Basic Auth as username/app-specific-password.
+
+To enhance security Bitbucket offers optional Two-Factor Authentication (2FA). When 2FA is enabled username/password Basic Auth access to the REST APIs and to Git repositories is suspended.
+At that point users are left with the choice of username/apps-specific-password Basic Auth for REST APIs and Git interactions, OAuth for REST APIs and Git/Hg interactions or SSH for Git/HG interactions and one of the previous choices for REST APIs.
+SSH and REST API access are beyond the scope of this document.
+Read about [Bitbucket's 2FA implementation](https://confluence.atlassian.com/bitbucket/two-step-verification-777023203.html).
+
+App-specific passwords are not particularly user friendly as once created Bitbucket hides their value, even from the owner.
+They are intended for use within application that talk to Bitbucket where application can remember and use the app-specific-password.
+[Additional information](https://confluence.atlassian.com/display/BITBUCKET/App+passwords).
+
+OAuth is the intended authentication method for user interactions with HTTPS remote URL for Git repositories when 2FA is active.
+Essentially once a client application has an OAuth access token it can be used in place of a user's password.
+Read more about information [Bitbucket's OAuth implementation](https://confluence.atlassian.com/bitbucket/oauth-on-bitbucket-cloud-238027431.html).
+
+Bitbucket's OAuth implementation follows the standard specifications for OAuth 2.0, which is out of scope for this document.
+However it implements a comparatively rare part of OAuth 2.0 Refresh Tokens.
+Bitbucket's Access Token's expire after 1 hour if not revoked, as opposed to GitHub's that expire after 1 year.
+When GitHub's Access Tokens expire the user must anticipate in the standard OAuth authentication flow to get a new Access Token. Since this occurs, in theory, once per year this is not too onerous.
+Since Bitbucket's Access Tokens expire every hour it is too much to expect a user to go through the OAuth authentication flow every hour.
+Bitbucket implements refresh Tokens.
+Refresh Tokens are issued to the client application at the same time as Access Tokens.
+They can only be used to request a new Access Token, and then only if they have not been revoked.
+As such the support for Bitbucket and the use of its OAuth in the Git Credentials Manager differs significantly from how VSTS and GitHub are implemented.
+This is explained in more detail below.
+
+## Multiple User Accounts
+
+Unlike the GitHub implementation within the Git Credential Manager, the Bitbucket implementation stores 'secrets', passwords, app-specific passwords, or OAuth tokens, with usernames in the [Windows Credential Manager](https://msdn.microsoft.com/en-us/library/windows/desktop/aa374792(v=vs.85).aspx) vault.
+
+Depending on the circumstances this means either saving an explicit username in to the Windows Credential Manager/Vault or including the username in the URL used as the identifying key of entries in the Windows Credential Manager vault, i.e. using a key such as `git:https://mminns@bitbucket.org/` rather than `git:https://bitbucket.org`.
+This means that the Bitbucket implementation in the GCM can support multiple accounts, and usernames,  for a single user against Bitbucket, e.g. a personal account and a work account.
+
+## Authentication User Experience
+
+When the GCM is triggered by Git, the GCM will check the `host` parameter passed to it.
+If it contains `bitbucket.org` it will trigger the Bitbucket related processes.
+
+### Basic Authentication
+
+If the GCM needs to prompt the user for credentials they will always be shown an initial dialog where they can enter a username and password. If the `username` parameter was passed into the GCM it is used to pre-populate the username field, although it can be overridden.
+When username and password credentials are submitted the GCM will use them to attempt to retrieve a token, for Basic Authentication this token is in effect the password the user just entered.
+The GCM retrieves this `token` by checking the password can be used to successfully retrieve the User profile via the Bitbucket REST API.
+
+If the username and password credentials sent as Basic Authentication credentials works, then the password is identified as the token. The credentials, the username and the password/token, are then stored and the values returned to Git.
+
+If the request for the User profile via the REST API fails with a 401 return code it indicates the username/password combination is invalid, nothing is stored and nothing is returned to Git.
+
+However if the request fails with a 403 (Forbidden) return code, this indicates that the username and password are valid but 2FA is enabled on the Bitbucket Account.
+When this occurs the user it prompted to complete the OAuth authentication process.
+
+### OAuth
+
+OAuth authentication prompts the User with a new dialog where they can trigger OAuth authentication.
+This involves opening a browser request to `_https://bitbucket.org/site/oauth2/authorize?response_type=code&client_id={consumerkey}&state=authenticated&scope={scopes}&redirect_uri=http://localhost:34106/_`.
+This will trigger a flow on Bitbucket where the user must login, potentially including a 2FA prompt, and authorize the GCM to access Bitbucket with the specified scopes.
+The GCM will spawn a temporary, local webserver, listening on port 34106, to handle the OAuth redirect/callback.
+Assuming the user successfully logins into Bitbucket and authorizes the GCM this callback will include the Access and Refresh Tokens.
+
+The Access and Refresh Tokens will be stored against the username and the username/Access Token credentials returned to Git.
+
+# On-Premise Bitbucket
+
+On-premise Bitbucket, more correctly known as Bitbucket Server or Bitbucket DC, has a number of differences compared to the cloud instance of Bitbucket, https://bitbucket.org. 
+
+As far as GCMC is concerned the main difference it doesn't support OAuth so only Basic Authentication is available.
+
+It is possible to test with Bitbucket Server by running it locally using the following command from the Atlassian SDK:
+
+	❯ atlas-run-standalone --product bitbucket
+
+See https://developer.atlassian.com/server/framework/atlassian-sdk/atlas-run-standalone/.
+
+This will download and run a standalone instance of Bitbucket Server which can be accessed using the credentials `admin`/`admin` at
+
+	https://localhost:7990/bitbucket

src/shared/Atlassian.Bitbucket.Tests/BitbucketHostProviderTest.cs

@@ -0,0 +1,60 @@
+using Microsoft.Git.CredentialManager;
+using Microsoft.Git.CredentialManager.Tests.Objects;
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Net.Http;
+using System.Text;
+using System.Threading.Tasks;
+using Xunit;
+
+namespace Atlassian.Bitbucket.Tests
+{
+    public class BitbucketHostProviderTest
+    {
+        [Theory]
+        // We report that we support unencrypted HTTP here so that we can fail and
+        // show a helpful error message in the call to `GenerateCredentialAsync` instead.
+        [InlineData("http", "bitbucket.org", true)]
+        [InlineData("ssh", "bitbucket.org", false)]
+        [InlineData("https", "bitbucket.org", true)]
+        [InlineData("https", "api.bitbucket.org", true)] // Currently does support sub domains.
+
+        [InlineData("https", "bitbucket.ogg", false)] // No support of phony similar tld.
+        [InlineData("https", "bitbucket.com", false)] // No support of wrong tld.
+        [InlineData("https", "example.com", false)] // No support of non bitbucket domains.
+
+        [InlineData("http", "bitbucket.my-company-server.com", false)]  // Currently no support for named on-premise instances
+        [InlineData("https", "my-company-server.com", false)]
+        [InlineData("https", "bitbucket.my.company.server.com", false)]
+        [InlineData("https", "api.bitbucket.my-company-server.com", false)]
+        [InlineData("https", "BITBUCKET.My-Company-Server.Com", false)]
+        public void BitbucketHostProvider_IsSupported(string protocol, string host, bool expected)
+        {
+            var input = new InputArguments(new Dictionary<string, string>
+            {
+                ["protocol"] = protocol,
+                ["host"] = host,
+            });
+
+            var provider = new BitbucketHostProvider(new TestCommandContext());
+            Assert.Equal(expected, provider.IsSupported(input));
+        }
+
+        [Theory]
+        [InlineData("X-AREQUESTID", "123456789", true)] // only the specific header is acceptable
+        [InlineData("X-REQUESTID", "123456789", false)]
+        [InlineData(null, null, false)]
+        public void BitbucketHostProvider_IsSupported_HttpResponseMessage(string header, string value, bool expected)
+        {
+            var input = new HttpResponseMessage();
+            if (header != null)
+            {
+                input.Headers.Add(header, value);
+            }
+
+            var provider = new BitbucketHostProvider(new TestCommandContext());
+            Assert.Equal(expected, provider.IsSupported(input));
+        }
+    }
+}

src/shared/Atlassian.Bitbucket/BitbucketHostProvider.cs

@@ -66,8 +66,12 @@ public bool IsSupported(HttpResponseMessage response)
                 return false;
             }
 
-            // TODO: identify Bitbucket on-prem instances from the HTTP response
-            return false;
+            // Identify Bitbucket on-prem instances from the HTTP response using the Atlassian specific header X-AREQUESTID
+            var supported =  response.Headers.Contains("X-AREQUESTID");
+
+            _context.Trace.WriteLine($"Host is{(supported ? null : "n't")} supported as Bitbucket");
+
+            return supported;
         }
 
         public async Task<ICredential> GetCredentialAsync(InputArguments input)