fix: specify content type when validating OIDC

[achmelo]

Description

ZAAS service rejects validation request when content is not specified.

Linked to # (issue)
Part of the # (epic)

Type of change

Please delete options that are not relevant.

• fix: Bug fix (non-breaking change which fixes an issue)
• feat: New feature (non-breaking change which adds functionality)
• docs: Change in a documentation
• refactor: Refactor the code
• chore: Chore, repository cleanup, updates the dependencies.
• BREAKING CHANGE or !: Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• My code follows the style guidelines of this project
• PR title conforms to commit message guideline ## Commit Message Structure Guideline
• I have commented my code, particularly in hard-to-understand areas. In JS I did provide JSDoc
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• The java tests in the area I was working on leverage @nested annotations
• Any dependent changes have been merged and published in downstream modules

For more details about how should the code look like read the Contributing guideline

[sonarcloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[Shobhajayanna]

LGTM