Open Payments + Rafiki: client to resource server request signing

[matdehaast]

Summary

GNAP tokens are not bearer tokens and therefore require the client to sign requests to the resource server with its private key. These signatures should then be presented to resource server as per the GNAP spec.

Intended Outcomes

• Documentation within open payments spec/website so that implementors can correctly make requests.
• Implementation in Rafiki

Links

• https://github.com/interledger/open-payments/issues/163
• https://github.com/interledger/rafiki/issues/585