Authentication selectors provide a plugin capability for PingFederate to evaluate various conditions related to the requests. PingFederate comes bundled with a set of authentication selectors. for example, you can create an HTTP Header Authentication Selector to detect mobile browsers, a CIDR Authentication Selector to evaluate whether the users' IP addresses fall within your internal network ranges, or an HTTP Request Parameter Authentication Selector to identify IdP connections based on the PartnerIdpId parameter values provided in the SP-initiated SSO requests.
Alternatively, you can create custom authentication selectors that suit your needs by using the PingFederate SDK.
The Javadoc for PingFederate is located in the <pf_install>/pingfederate/sdk/doc directory.