Unfortunately, I have some bad news. I created an initial integration using the Dexcom API and realized it’s only a retrospective API and has a 3-hour delay.
There’s an unofficial API used by Home Assistant in GitHub - gagebenne/pydexcom: A simple Python API to interact with Dexcom Share service which is realtime, but it would require users to enter their username and password. That would not be secure, and I imagine a PR would not be accepted by the Tidbyt team. 
I’ll see if that API requires creating a separate read-only Dexcom Share user. If so, then it would maybe be acceptable.
Grr, from that repo:
- Note: the service requires setup of at least one follower to enable the share service, but
pydexcomwill use your credentials, not the follower’s.
This may not be doable in a secure way.
I know you mentioned not wanting to set up a Nightscout server, but that may be your best bet. There are some pretty helpful guides out there, and Nightscout can be set up to scrape data from Dexcom directly.
I’ll let you know if I come across anything else!