Hi Clay Casper,
Update: I heard back from the product team. You are correct that Azure does not support pattern matching for the branch entity type when adding a federated credential to an application registration.
This is a limitation that the product team is aware of, and they are working on a fix. There is a design planned for this with the intent of fixing the way that this limitation affects Github branching. It is being worked on currently but the ETA may change based on a number of variables. I will update this thread if I hear more.
In the meantime, you are also welcome to leave a feature request in the Feedback forum so that the product team can reply directly there as well: [https://feedback.azure.com/
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