(Forked from #39.)

There are several use cases for transmitting a certificate chain alongside the signature. We should either:

• Add a certificate field with clearly defined semantics that avoids known pitfalls; or
• Reject this idea and add a FAQ explaining what alternatives we recommend.

Personally I have no objections to adding a field, but I'd like to hear from others to explain what the concerns are.

/cc @trishankatdatadog @laurentsimon @shizhMSFT @gokarnm @TomHennen @dlorenc