It should be possible to do this w/ eBPF. Monitor network i/o & rewrite the request on the fly to include the proper tokens & signatures. The agent can just be given placeholder tokens. That way all the usual libraries work as expected & the secrets/signatures are handled w/o worrying about another abstraction layer. Here is some prior art:
https://riptides.io/blog/when-ebpf-isnt-enough-why-we-went-w...