[jakelazaroff]

If OP isn't allowing third parties to authenticate through their API there's really no reason to use OAuth.

[kevlened]

To echo a sibling comment [0], if you don't use OAuth2 (or the OpenID Connect profile), you'll end up reimplementing similar functionality. There are libraries for OAuth2/OpenID Connect, while a custom authentication strategy requires more effort.

[0] https://news.ycombinator.com/item?id=16519660