The correct answer is 'Implementing SSL/TLS certificates'. SSL/TLS certificates enable secure connections through HTTPS by using a PKI to authenticate the server's identity to the client's browser and encrypt the data transmitted between them. This prevents eavesdropping and man-in-the-middle attacks. 'Using a web application firewall (WAF)' offers protection against web application attacks but does not inherently secure the communication channel. 'Implementing a virtual private network (VPN)' secures a connection between two points, primarily used for secure remote access rather than the secure browser-to-server communication desired here. 'Requiring multifactor authentication (MFA)' adds an additional layer of security for user authentication but does not address the secure channel of communication between the server and client.