Are you using classic esx? and not the ESXi. The reason I ask is because classic esx installation has reached end of life VMware KB: End of Availability and End of Support Life for ESX 4.x and VMware Management Assistant 1... - you might want to consider upgrading to later version ESXi which could potentially meet your security requirement.
Also this question has appeared in the past...check this forum SSH and Active Directory 2000
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vfk
Systems Manager / Technical Architect
VCP5-DCV, VCAP5-DCA, vExpert, ITILv3, CCNA, MCP