Add Charon Support for Beacon Node Authentication

[OisinKyne]

Description:
During testing with the GCP Blockchain Node Engine, we have identified a requirement to add authentication for accessing beacon nodes.
This enhancement will enable Charon to support authentication when interacting with authenticated beacon nodes.

Acceptance Criteria:

• Implement support for authenticating beacon nodes in Charon

• HTTP Header: Add support for passing an API key in an HTTP header. Supplied to charon via csv or similar formatted flag like: --beacon-node-headers=X-goog-api-key=xxxx

Testing:

• Verify authentication using the URI parameter method
• Verify authentication using the HTTP header method

Notes:

• Please document any configuration changes required for users to enable these authentication method

[OisinKyne]

A related issue was raised by the chain up team.

Hi obol team

I found that one of charon's dependency libraries, go-eth2-client, had a code commit on 2024.07.25, as shown below

When setting beaconAddr, the path path of the beacon node is replaced. In many cases, we will use an external beacon node with a token. This code makes the configured beacon node inaccessible and affects the experience.


https://github.com/attestantio/go-eth2-client/issues/173