Authelia

Authelia is an open-source authentication and authorization server and portal fulfilling the identity and access management (IAM) role of information security in providing multi-factor authentication and single sign-on (SSO) for your applications via a web portal. It acts as a companion for common reverse proxies. With a compressed container size smaller than 20 megabytes and observed memory usage normally under 30 megabytes, it's one of the most lightweight solutions available. Written in Go and React, authorization policies and many other backend tasks are completed in mere milliseconds and login portal loading times of 100 milliseconds makes it one of the fastest solutions available. Processors can use a lot of electricity, but when idle usage is basically so low that you can't measure it, and active usage in a small business environment being under 1% you can rest easy (with the exclusion of password hashing).