There does not seem to be a way to allow HTTP in the GUI or the ADM but it can be done in the registry.
- Open Regedit
- Navigate to HKLM\SOFTWARE\Citrix\AuthManager on a 32-bit machine or HKLM\SOFTWARE\Wow6432Node\Citrix\AuthManager on a 64-bit machine
- Under AuthManager create a new String Value (Reg_SZ) with the name ConnectionSecurityMode and the Data Any
- Navigate to HKEY_LOCAL_MACHINE\SOFTWARE\Citrix\Dazzle on a 32-bit machine or HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node\Citrix\Dazzle on a 64-bit machine
- Under Dazzle modify the data of AllowAddStore to be A
- Exit Citrix Receiver and restart it.