feat: support generic secret in docker auth

[quixoten]

Overview

currently, the webhook only supports unwrapping the value of the auth key if it's in a specific user:pass format. this limitation prevents the webhook from working correctly for other valid formats of the auth value, e.g., _json_key.

[csatib02]

Hey @quixoten, First of all thank you for your contribution! Vault-Secrets-Webhook, will no longer be maintained in the near future, because it will be replaced with our new Webhook project. I already added this feature to that one, but adding an e2e test-case for json_key handling seems reasonable, may I ask you to please take a look at Secrets-Webhook and if you have the time for it incorporate your changes regarding the e2e tests on that project?

In the meanwhile I left a few comments. Also, please sign your commits, there are instructions if you click on the failed DCO check.

[github-actions[bot]]

Thank you for your contribution! This PR has been automatically marked as stale because it has no recent activity in the last 60 days. It will be closed in 20 days, if no further activity occurs. If this pull request is still relevant, please leave a comment to let us know, and the stale label will be automatically removed.

[github-actions[bot]]

This PR has been marked stale for 20 days, and is now closed due to inactivity. If this contribution is still relevant, please re-open this PR or file a new one. Thank you!