FIX Pulsar pubsub component initialization when using oauth2ClientSecretPath

[MyMirelHub]

Description

Fixes oauth2ClientSecretPath (which previously incorrectly looked for token instead of client secret), offloads file loading to common client credentials library, and introduces oauth2CredentialsFile for loading client_id, client_secret, and issuer_url from a JSON file.

• oauth2ClientSecretPath: Fixed to load client secret from file (previously incorrectly looked for token)

• oauth2CredentialsFile: New field for loading client_id, client_secret, and issuer_url from a JSON file

  • JSON format: {"client_id": "...", "client_secret": "...", "issuer_url": "..."}

Implementation Details

• Offloaded file loading logic to common/authentication/oauth2 package
• Added LoadCredentialsFromJSONFile function for parsing JSON credential files
• Metadata fields override file values

Issue reference

#4162

Checklist

Please make sure you've completed the relevant tasks for this PR, out of the following list:

• Code compiles correctly
• Created/updated tests
• Extended the documentation
  • Created the dapr/docs PR: [1.17] docs for pulsar file auth docs#5004

[atrauzzi]

I feel like each supported format should be a separate field, for consistency and expectations. Also protects against the 🛸 future 🛸 in case we reach a point where there are too many scenarios to sort out?

[MyMirelHub]

I feel like each supported format should be a separate field, for consistency and expectations. Also protects against the 🛸 future 🛸 in case we reach a point where there are too many scenarios to sort out?

Agreed - we should split the paths/functions

      - name: oauth2CredentialsFile
        type: string
        description: |
          The path to a JSON file containing both client_id and client_secret.
        example: "/path/to/oauth2/credentials.json"

      - name: oauth2ClientSecretPath
        type: string
        description: |
          The path to a plain text file containing the OAuth Client Secret.
        example: "/path/to/oauth2/client_secret.txt"

[cicoyle]

Can you open a docs PR noting the metadata fields @MyMirelHub ?

[cicoyle]

Scratch that - docs PR is here