Upload a file via webfig.

Given a username and password, this function will authenticate with the remote router.

Negotiates encryption with the remote Webfig described by `webfigURL`.

this switch is cursed.

Provided an M2Message this function will apply the various paddings/headers, encrypt it, and send it to the remote target described by `webfigURL`.

WebfigSession tracks the crypto for a given "session" which is associated with an ID.