Add support to lib/secure to allow for encrpytion/decryption/signing of a server auth token
The authentication model in Sonador is based on bearer/API tokens. These values can be provided in an Authentication header that is sent to Sonador for validation and associated with a user.
There are many instances in the data model where the server itself needs to send commands to Orthanc and associated systems. The server should have a special token of its own (specified in the site configuration) that allows it to authenticate its own requests. (Use-case: Make authenticated calls to the Orthanc REST API.)
Because the value will be very sensitive, it should be encrypted and signed prior to attaching it to outbound requests.