Feature Request: Support credential injection with HTTP Connect

[danquack]

Is your feature request related to a problem? Please describe.
Utilizing an HTTP target it would be nice to be able to pass additional headers, specifically credential based headers to the backend.

Describe the solution you'd like
The current http connect methods use curl, but doesn't support either static or dynamic headers. I would like to either be able to pull a token or send basic auth from Vault, which then gets passed on.

Describe alternatives you've considered
Currently just use a TCP session and then provide credentials through an external process.

Explain any additional use-cases

• API Proxying
• Transparent sessions user authentication to backend app

Additional context
Add any other context or screenshots about the feature request here.