How to deploy an SSIS project having EncryptAllWithPassword

I have a PowerShell script that deploys an SSIS project to SSISDB. It works fine for projects using DontSaveWithSensitive protection but fails for projects using EncryptAllWithPassword.

The message in SSISDB.internal.operation_messages is "Failed to deploy the project. Fix the problems and try again later.:The encrypted data in project manifest failed to load. The project manifest is corrupted or if the project is password protected, the specified password is incorrect." (id=380696).

The code I use reads the isPac file, then deploys the project:

[byte[]] $projectFile = [System.IO.File]::ReadAllBytes($isPac)
$project = $folder.DeployProject($proj, $projectFile)

(This code fragment shows up in most examples I have found.)

The DeployProject() method fails. It does not appear to have a mechanism for accepting the password required to perform the decryption.

Any ideas on how the SSDT deployment wizard handles this? Or other strategies?

Thanks.