1. A system for handling unexpected content at a client-side application, comprising: a computer comprising a processor; and instructions which are executable, using the processor, to implement functions comprising: sending, from a client-side application, a content request to a server for which a gateway provides access protection, the content request adapted for requesting a content fragment from the server; receiving, at the client-side application from the gateway, a response message sent from the gateway to the client-side application responsive to the gateway determining that the requested content fragment is access-protected; inspecting the response message, at the client-side application, to determine whether the response message contains the requested content fragment; responsive to determining, at the client-side application, that the response message contains the requested content fragment, processing the requested content fragment contained in the response message; and responsive to determining, at the client-side application, that the response message comprises a request message containing unexpected content, the unexpected content comprising content which differs from the requested content fragment, dynamically constructing a prompt for the client-side application to respond to the request message containing the unexpected content, the client-side application lacking a predefined prompt for handling the unexpected content, comprising: creating a user input frame; inserting the unexpected content from the request message into the user input frame; displaying the user input frame; obtaining a user response from the displayed user input frame; and returning the obtained user response from the client-side application to the gateway as a response to the request message.