Scope mapping for proxy / additional header does not work any more with 2025.10.0

[troem]

Describe the bug
We defined the following scope mapping and added it to an proxy-provider:

token = request.user.attributes.get("influxdbtoken")

return {
    "ak_proxy": {
        "user_attributes": {
            "additionalHeaders": {
                "Authorization": f"Bearer {token}"
            }
        }
    }
}

To Reproduce
Steps to reproduce the behavior:

1. Create the scope mapping within "Customization - Property Mappings"
2. Add the scope to your proxy provider
3. Check the headers, no "Authorization" is added to the request

Expected behavior
Scope mapping should still work and add extra headers to the request

Version and Deployment (please complete the following information):

• authentik version:2025.10.0
• Deployment: docker-compose

[dominic-r]

Thanks for opening this issue, we'll investigate and open a PR for the next patch release if needed

[rissson]

Potentially offending PR #17650
Potentially related to #17750