Notify the host application to handle a SSL client certificate request. The host application is responsible for showing the UI if desired and providing the keys. There are three ways to respond: proceed(), cancel() or ignore(). Webview remembers the response if proceed() or cancel() is called and does not call onReceivedClientCertRequest() again for the same host and port pair. Webview does not remember the response if ignore() is called. This method is called on the UI thread. During the callback, the connection is suspended. The default behavior is to cancel, returning no client certificate.

[Android Documentation]