When integrating Salesforce with an external system that does not support HTTP-basic authentication, what approach should be recommended?

The most suitable approach when integrating Salesforce with an external system that does not support HTTP-basic authentication is to digitally sign the payload with a trusted private key. This method enhances security by ensuring that the data being sent is authentic and has not been altered in transit. Digital signatures provide non-repudiation benefits, meaning that the sender cannot deny having sent the message, as it can be verified using the sender's public key.

In scenarios where basic authentication is not available, relying on digital signatures can help establish trust between the systems without needing user credentials directly included in the communication. Furthermore, using a private key for signing adds an additional layer of security, as only the trusted party possesses the key necessary to create the signature, while the recipient can validate the signature using the corresponding public key.

The other approaches do not effectively address the issue of authentication for secure data transmission or lack sufficient security measures. For instance, using a validated secret passphrase in the payload could expose sensitive information to anyone intercepting the message. Base64 encoding only obscures the visibility of the data but does not provide encryption or authentication, leaving the data potentially vulnerable. Utilizing a third-party Single Sign-On (SSO) solution could complicate the integration process rather than simplifying it, as it