Implementing function metadata transform support

[liliankasem]

Issue describing the changes in this PR

resolves #issue_for_this_pr

Pull request checklist

• My changes do not require documentation changes
  • Otherwise: Documentation issue linked to PR
• My changes should not be added to the release notes for the next release
  • Otherwise: I've added my notes to release_notes.md
• My changes do not need to be backported to a previous version
  • Otherwise: Backport tracked by issue/PR #issue_or_pr
• I have added all required tests (Unit tests, E2E tests)

Additional information

Rough draft of feature to allow augmentation of the FunctionMetadata.

Works E2E with: Azure/azure-functions-mcp-extension#88

[jviau]

Interesting approach. We should discuss this a bit more. I have an existing draft PR (#2834) and issue (#1159) that this approach would also address.

[mattchenderson]

PR should be retitled / commit message for squash-and-merge should be adjusted so that history does not include a reference to a type not being included.

[jviau]

Need to make sure to update AspNetCore extension to consume IFunctionMetadataManager and not the provider.

[alanlima]

Hi @liliankasem

That’s a really interesting approach and implementation.

I’m currently working on a similar requirement where I need to implement a custom metadata provider to support disabling functions in the staging slot. I’ve successfully migrated to the new Metadata Transformer, which has been great.

However, I’m curious about one aspect: why is the Transform method synchronous (sync) when the GetFunctionMetadataAsync method in the metadata provider is asynchronous (async)?

In our use case, we disable functions using feature flags via IFeatureManager, aiming to replicate the behaviour of the FeatureGateAttribute used in ASP.NET applications. Since IFeatureManager relies on async methods, applying this requirement forces us into a sync over async scenario — which is less than ideal.

Would love to hear your thoughts on this design decision and whether there’s any guidance or workaround you’d recommend.