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node-oauth2-server
Complete, compliant and well tested module for implementing an OAuth2 Server/Provider with express in node.js
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SurveyJS
Open-Source JSON Form Builder to Create Dynamic Forms Right in Your App. With SurveyJS form UI libraries, you can build and style forms in a fully-integrated drag & drop form builder, render them in your JS app, and store form submission data in any backend, inc. PHP, ASP.NET Core, and Node.js.
So aside from that, there's things like oauth-server which does actually allow you to implement an authorization server. So, if you yourself have a database of users that you want third party clients to be able to authenticate against, you can create your own identity server and implement the various flows.... or maybe you have umpteen systems all with their own auth schemes and you want to standardize it - oauth can be used to centralize this authorization.