WebDriver capabilities are used to communicate the features supported by a WebDriver session.
When a WebDriver session is created it returns a set of capabilities describing the negotiated, effective capabilities of the session. Some of the capabilities included in this set are standard and shared between all browsers, but the set may also contain browser-specific capabilities and these are always prefixed.
acceptInsecureCertscapability communicates whether expired or invalid TLS certificates are checked when navigating. If the capability is false, an insecure certificate error will be returned. Otherwise self-signed or otherwise invalid certificates will be implicitly trusted by the browser on navigation. The capability has effect for the lifetime of the session.
In addition to the standard capabilities WebDriver allows third-parties to extend the set of capabilities to match their needs. As we’ve learned, the capabilities negotiation is rather strict: unless all the requested capabilities to start a new session matches, the driver will refuse to start and return with a session not created error.