web3signer doesn't set appropriate headers to indicate that json is an acceptable response

[lrusak]

Description

The web3signer doesn't set the applicable Accept header to indicate that application/json is an acceptable response.

the web3signer api indicates that both application/json and text/plain are acceptable response types for signing requests.

The web3signer handler in lighthouse requires a json response. Setting the header "Accept: application/json" indicates to the web3signer that json is an acceptable response.

The default header uses Accept: */* which means any response is acceptable.

Version

stable (v5.1.3)

Present Behaviour

Fail to deserialize response as json if the respnse return type is plain/text.

Expected Behaviour

Properly deserialize the json response

Steps to resolve

Set the correct header for the request.