About autolinks
Anyone with admin permissions to a repository can configure autolink references to link issues, pull requests, commit messages, and release descriptions to external third-party services.
Configuring autolinks to reference external resources
This procedure demonstrates how to configure autolinks to reference external resources. For example, if you use Zendesk to track user-reported tickets, you can reference a ticket number in the pull request you opened to fix the issue.
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On your GitHub Enterprise Server instance, navigate to the main page of the repository. 
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Under your repository name, click Settings.  
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In the left sidebar, click Autolink references.  
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Click Add autolink reference.   
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Under "Reference prefix", type a short, meaningful prefix you want collaborators to use to generate autolinks for the external resource.  
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Under "Target URL", type the link to the external system you want to link to. Use the <num>variable as a placeholder for the reference identifier. 
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Click Add autolink reference. 