Description of problem:

When using the OwnedEntityPicker field in a Backstage scaffolder template, users who belong to many groups (35+ groups with long names) encounter a 431 "Request Header Fields Too Large" HTTP error when the template contains multiple catalogFilter entries.

Prerequisites (if any, like setup, operators/versions):

Steps to Reproduce

1. Create a user that belongs to 35+ groups with long names (e.g., group-001-abcdefghijklmnopqrstuv through group-036-abcdefghijklmnopqrstuv)

2. Configure authentication to include all group membership in the user's ownedEntityRefs:

• guest provider:

  auth:
    providers:
      guest:
        userEntityRef: user:default/testuser
        ownershipEntityRefs:
          - user:default/testuser
          - group:default/group-001-abcdefghijklmnopqrstuv
          - group:default/group-002-abcdefghijklmnopqrstuv

3. Create a scaffolder template with OwnedEntityPicker field containing multiple catalogFilter entries:  

 ownedEntity:
     title: Entities
     type: string
     "ui:field": OwnedEntityPicker
     "ui:options":
       catalogFilter:
       - kind: component
         metadata.namespace: system1
       - kind: component
         metadata.namespace: system2
       - kind: component
         metadata.namespace: system3
         # add more filters if needed
 

4. Access the scaffolder template as the user with many groups

5. The OwnedEntityPicker will fail with a 431 error when trying to fetch entities. (see Network tab).

Actual results:

The OwnedEntityPicker will not display any values and in network tab you can notice a 431 error when trying to fetch entities.

Expected results:

The OwnedEntityPicker should display the entities that the user (or his group) owns.

Reproducibility (Always/Intermittent/Only Once):

Always

Build Details:

1.7, 1.8 and 1.9 

Additional details:

I can reproduce this issue in Backstage.

Additional info (Such as Logs, Screenshots, etc):