Support for Service Principals and Azure Managed Identities in Azure DevOps

[ausfestivus]

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• [ ] I'd be willing to implement this feature (contributing guide)

Describe the user story As an operator of our organisation's Atlantis instance, I would like to configure Atlantis to integrate with Azure DevOps using its new support for Service Principals and Managed Identities. This is so I can integrate Atlantis on ACI with AzDO using modern authentication and authorisation patterns.

Describe the solution you'd like AzDO support for Service Principals and Managed Identities was announced last week. https://learn.microsoft.com/en-gb/azure/devops/release-notes/2023/sprint-219-update#service-principal-and-managed-identity-support-in-azure-devops. The WHY is described in the blog post at https://devblogs.microsoft.com/devops/introducing-service-principal-and-managed-identity-support-on-azure-devops/. The documentation for the new feature is available in https://learn.microsoft.com/en-us/azure/devops/integrate/get-started/authentication/service-principal-managed-identity?view=azure-devops&preserve-view=true

Describe the drawbacks of your solution ACI is not currently able to run Atlantis containers newer than the v0.22.3 release. See https://github.com/runatlantis/atlantis/issues/3291

Describe alternatives you've considered Alternatices are not available in our org. Our org is a Microsoft shop. Azure services are all that are available currently.

[jamengual]

@ausfestivus fell free to propose a PR