I'm trying to use a SDB user to register a station using the dashboard tool.

CTI user administered for "Unrestricted Access" via the "Edit CTI User" web page on the AE Services Management Console.

The goal is to register and control a device without using his defined password.
I observed that:
a) if VALUE_AES_DMCC_DMC field is not present as part of the AES license AND empty password is used for that extension, the registration fails:
<code>3000</code>
<reason>Registration Reject reason: securityDenial
Login Denied - Access Code invalid. diagnostic string= code= 63773</reason>

b) if VALUE_AES_DMCC_DMC field is not present as part of the AES license AND password is provided, registration is okay.

I thought that field ( VALUE_AES_DMCC_DMC ) will be necessary in both cases ( empty password or not ). Or VALUE_AES_DMCC_DMC is not actually necessary when the client application does know the extension password to register a device?

As a legacy fall back if there are no available VALUE_AES_DMCC_DMC licenses, AES checks with Communication Manger to see if any IP_API_A licenses are available. If so the IP_API_A license takes the place of the VALUE_AES_DMCC_DMC license. So assuming you have IP_API_A licenses on Communication Manager (which is highly likely if you have IP stations), then this makes sense to me.

Thanks.
So IP_API_A license will be consumed when extension password is used (eg: extension 40010 with pass "123456"), but same license is not required for empty password (eg: 40010/<empty>)?

Hope I understood correctly.

No, a license, either IP_API_A or VALUE_AES_DMCC_DMC must be available, and is consumed when a DMCC device registration is successful.