ODK Central without HTTPS

1. What is the issue? Please be detailed.
I have ODK Central installed on a private local network (with no internet access), so no possibility of using a domain name with a CA signed SSL certificate. Before I explore using a custom ODK Collect build with a self-signed certificate (which I want to avoid unless absolutely necessary), I would like to understand if it is possible to configure ODK Central to be accessible over HTTP, instead of HTTPS.
In either case, the plan is to explore connecting ODK Collect to Central using mDNS over local WiFi on linux (with avahi daemon).

I have reviewed prior topics on SSL, self signed certificates etc., but none was specifically exploring the use of ODK Collect w/ Central over plain HTTP.
Any inputs much appreciated ! This project is for local schools in my school district in India that I am executing as part of the non-profit I work with.
Regards,
Chandra

I don't think HTTP access is possible easily cuz ODK Central (check the NGINX config for the same here) tries to enforce secure HTTPS access.

If I were in your place:

Step 1: I would stick with HTTPS with a self-signed certificate.
Step 2: I would install ODK Central locally, the way you recommended - mDNS and stuff.
Step 3: I would re-configure Enketo to make it work locally if necessary.
Step 4: Lastly, I would install my self-signed certificates on the android device used for data collection in order to allow ODK Collect to function with no issue.

PS: I haven't tested it all yet, just my thoughts for how I would proceed.