Cross-Tenant subscription deployments

**Is your feature request related to a problem? Please describe.**
We have multiple customer cases, where we need to deploy VMs based on ARM/Bicep templates with image references. These images are located in a Azure Compute Library in another tenant and have a specific, second service principal they use to authenticate.
The docs doesn't mention this scenario, only using CLI and PowerShell to realize cross-tenant access. Also, the parameters `aux-tenants` and `aux-subs` from `az deployment group` are not available in `az deployment sub`.

**Describe the solution you'd like**
We need a solution where we can specify a second service principal and tenant to authenticate against the compute gallery. The reference to the image is already in resource id format. This has to be provided either as a parameter in Bicep(maybe with scopes) or as a azure cli parameter.

**Describe alternatives you've considered**
Afaik there are no alternatives available, if you want to use IaC with ARM or Bicep