(If this PR fixes a github issue, please add Fixes #<xyz>.)

Fixes streamnative/pulsarctl#1266 which uses the code being touched here.

Motivation

As the issue shows when using Pulsarctl which works with a context as configuration style, Oauth2 is used under the hood.

However the library does not expose any way to inject the context configuration scope value, and then relies on reading that from the keyFile for client_credentials flow.

However that is not being utilized in the current code as the scope value is not read from from the file.

Explain here the context, and why you're making that change. What is the problem you're trying to solve.
To allow the usage of oauth2 with a keyfile in Pulsarctl 3+ which it doesn't right now

Modifications

Describe the modifications you've done.

Alters so reading the keyFile for client credentials also returns the scope value.

The value is then split on spaces, and added to a temporary slice.
After that the value of any additionalScopes that was already in the options is then added to the temp slice as well.
In the end the additionalScopes property on the options is set to the temp slice containing values from previous additionalScopes and the ones from the keyFile.

Verifying this change

• Make sure that the change passes the CI checks.

(Please pick either of the following options)

This change is a trivial rework / code cleanup without any test coverage.

(or)

This change is already covered by existing tests, such as (please describe tests).

(or)

This change added tests and can be verified as follows:

(example:)

• Added integration tests for end-to-end deployment with large payloads (10MB)
• Extended integration test for recovery after broker failure

Does this pull request potentially affect one of the following parts:

If yes was chosen, please highlight the changes

• Dependencies (does it add or upgrade a dependency): (yes / no)
• The public API: (yes / no)
• The schema: (yes / no / don't know)
• The default values of configurations: (yes / no)
• The wire protocol: (yes / no)

Documentation

• Does this pull request introduce a new feature? (yes / no)
• If yes, how is the feature documented? (not applicable / docs / GoDocs / not documented)
• If a feature is not applicable for documentation, explain why?
• If a feature is not documented yet in this PR, please create a followup issue for adding the documentation