Add ecall for requesting data using an execution token sent over a protected channel.

[longtomjr]

• OCall to the auth_enclave to validate and "use" the execution token (use protected channel)
• Return error if the token is invalid
• If token is valid, open and unseal the requested data and re-seal it to be sent back to the execution enclave.
• Check that the sealed data size is the same size as the buffer allocated by the caller.
• If the size match, return the sealed buffer

Blocked by: #74

Blocks: #72