This is community documentation for the API. To see official documentation, review zoneminder.readthedocs.org
Basic API Test (1.32.3)
Use this command to confirm the API is working.
curl -X POST -d "user=somename&pass=somepass" http://serverip/zm/api/host/getVersion.json
Make sure all of this is included. It is not necessary to use login.json before running this command. The ampersand must be between user and pass.
Related to the API, if you wish to have some encryption, refer to /etc/apache2/ports.conf You will see that it requires the ssl module, and the symbolic link.
Add the symbolic link for /etc/apache2/sites-available/default-ssl.conf to sites-enabled.
And uncomment / enable SSLEngine, SSLCertificateKey, and SSLCertificateKeyFile in /etc/apache2/sites-available/default-ssl.conf.
You may optionally want to generate a new SSL key.
Setting up self signed SSL certs for apache2 is a common sysadmin task. Search online for more info.