Geoserver

http://geoserver.org/about/

Installation:
(https://docs.geoserver.org/stable/en/user/installation/index.html#installation)
Tip for macos users using zsh. Put the ENV variable in your ~/.zshrc file with:
export PATH="GEOSERVER_HOME=/usr/local/geoserver:$PATH"

Once installed and the server is running via the website instructions the default username and password for a Geoserver is:

User name: admin
Password: geoserver

The following link is a good starting point for learning Geoserver:
https://docs.geoserver.org/stable/en/user/gettingstarted/index.html

WFS API on Geoserver
https://docs.geoserver.org/latest/en/user/services/wfs/reference.html

You build the request to the Geoserver using ol.format.WFS().writeGetFeature and then sending a get request to the Geoserver. For WFS and WMS you would direct it to these URLs for example (if you were working locally).
http://localhost:8080/geoserver/wfs
http://localhost:8080/geoserver/wms

The APIs are explained in this URL:
https://docs.geoserver.org/stable/en/user/services/wfs/reference.html

CQL
https://docs.geoserver.org/stable/en/user/filter/ecql_reference.html#ecql-expr

queries:https://docs.geoserver.org/stable/en/user/tutorials/cql/cql_tutorial.html
http://docs.opengeospatial.org/is/12-168r6/12-168r6.html

Authentication
https://docs.geoserver.org/maintain/en/user/security/passwd.html
https://geoserver.geo-solutions.it/educational/en/security/jdbc_authentication.html
https://geoserver.geo-solutions.it/educational/en/adv_gsconfig/parameters.html#wfs-resource-limits