What security feature is required with the SOAP API?

The requirement of Transport Layer Security (TLS) protocol with the SOAP API is fundamental because it ensures secure communication over the internet. TLS encrypts the data transmitted between the client and the Salesforce server, protecting sensitive information from eavesdropping and tampering while in transit. This layer of security is crucial for maintaining the integrity and confidentiality of the data being exchanged, especially when dealing with customer information or sensitive corporate data.

The other options, while potentially relevant to securing an application or service environment, do not serve the same specific role as TLS in the context of the SOAP API. Firewall protection helps to monitor and control incoming and outgoing network traffic but does not directly secure the data itself during its transmission. Two-factor authentication enhances user access security but does not apply to the data being transferred via the API. IP whitelisting restricts access based on IP addresses, adding a layer of security, but it does not address the encryption of data in transit. Thus, TLS stands out as the essential feature specifically required for the secure operation of the SOAP API.