title: How to authenticate to a private Github submodule in a VSTS automated build?
body: <p>I have a repository hosted on VSTS. That repository has a private github repository as a submodule. I have checkout submodules enabled.</p>
  
  <p><a href="https://i.stack.imgur.com/EdOaf.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/EdOaf.png" alt="Repo configuration"></a></p>
  
  <p>...</p>
  
  <p><a href="https://i.stack.imgur.com/tWYNN.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/tWYNN.png" alt="Checkout submodules"></a></p>
  
  <p>Using the Hosted MacOS pool to run the build, it fails because it can't authenticate to github:</p>
  
  <pre><code>2018-06-26T23:06:55.8029470Z Cloning into '/Users/vsts/agent/2.134.2/work/1/s/repo'...
  2018-06-26T23:06:56.2379010Z fatal: could not read Username for 'https://github.com': terminal prompts disabled
  2018-06-26T23:06:56.2405350Z fatal: clone of 'https://github.com/team/repo' into submodule path '/Users/vsts/agent/2.134.2/work/1/s/repo' failed
  2018-06-26T23:06:56.2419340Z Failed to clone 'repo'. Retry scheduled
  2018-06-26T23:06:56.2486770Z Cloning into '/Users/vsts/agent/2.134.2/work/1/s/repo'...
  2018-06-26T23:06:56.5982310Z fatal: could not read Username for 'https://github.com': terminal prompts disabled
  2018-06-26T23:06:56.6006440Z fatal: clone of 'https://github.com/team/repo' into submodule path '/Users/vsts/agent/2.134.2/work/1/s/repo' failed
  2018-06-26T23:06:56.6020680Z Failed to clone 'repo' a second time, aborting
  </code></pre>
  
  <p>There doesn't seem to be a place to put a Github personal access token if the main repository itself is not from Github.</p>
  
  <p>I can workaround this by creating my own MacOS build agent, and storing the github credential in the system credential manager. Is there a way to do this without having to create my own build agent?</p>