sign
Sign data with the specified key.
Called when a remote server requests a signature. The provider should:
Verify the request is legitimate (check context)
Optionally prompt the user for approval
Return the signature, or a successful null value to deny the request
Return
Successful SSH-encoded signature blob, successful null to refuse, or AgentResult.Failure if the provider could not process the request
Parameters
context
Rich context about the signing request