You can configure the iSCSI SAN to use CHAP authentication.

In CHAP authentication, when the initiator contacts an iSCSI target, the target sends a predefined ID value and a random value, or key, to the initiator. The initiator creates a one-way hash value that it sends to the target. The hash contains three elements: a predefined ID value, the random value that the target sends, and a private value, or CHAP secret, that the initiator and target share. When the target receives the hash from the initiator, it creates its own hash value by using the same elements and compares it to the initiator’s hash. If the results match, the target authenticates the initiator.

ESXi supports unidirectional and bidirectional CHAP authentication for iSCSI. In unidirectional CHAP authentication, the target authenticates the initiator, but the initiator does not authenticate the target. In bidirectional CHAP authentication, an additional level of security enables the initiator to authenticate the target.

ESXi supports CHAP authentication at the adapter level, when only one set of authentication credentials can be sent from the host to all targets. It also supports per-target CHAP authentication, which enables you to configure different credentials for each target to achieve greater target refinement.

See the vSphere Storage documentation for information about how to work with CHAP.