I found doing a custom (without a library) OAuth integration for only one service relatively straightforward, i.e. when it’s not treated as a standard. For exam

I found doing a custom (without a library) OAuth integration for only one service relatively straightforward, i.e. when it’s not treated as a standard. For example for a plug-in exclusively for Shopify (random example, didn’t try it) you would just treat it as the rest of their API and write custom code. In short it works when you can see it as a guideline instead of a standard.