Preliminary Seqexec Support

[swalker2m]

This PR is intended to open a conversation about what is needed to provide the seqexec with access to the new program model. Initially we need to be able to fetch observations from the ODB and then load them from the database.

I added a simple Service.queryObservationById(id: Observation.Id) method to complement ocs2.importObservation(host: String, oid: Observation.Id). In theory the seqexec can create a session by logging in and then use these two methods to obtain an observation containing a sequence.

I assume the observation you get back won't align exactly with what the seqexec needs but that's the next step. Also we'll eventually want the seqexec to write datasets and events back to the database and we'll need to provide the API for that as well.

[cquiroz]

How would you login?

[tpolecat]

How would you login?

gem needs to manage external users so it has its own user/role tables.

• An easy initial solution is to have a seqexec account that the seqexec uses, and provide the password to the seqexec on startup. I think this makes sense for the initial deployment.
• A better but harder solution is to federate with LDAP for authenticating gemini users and pass the operator's identity all the way through, and have all services use the exact same code to do this. We need this anyway but maybe not initially.

This assumes the seqexec talks to gem through some kind of network protocol. If it talks directly to the database then the game is different I think.