Provisioing Site Collections on-prem using the Tenant Admin API

Problem: Ability to provision Site Collections without using Server Side code.  Use CSOM and the Tenant Admin APIs.  This is a follow on the post: Provisioning Site Collections using CSOM (read it 1st).  Thanks to Sachin Khade, Frank M (check) and Alex N R (check) has given me his time to understand this: https://sachinkhade.wordpress.com/
I have reduced the Tenant Admin process into the least amount of steps that works.

The steps are:
Perform on an existing Web Application
Run the PS Script below:

1. Create SC using a team site site template STS#0
2. Set the AdministratorSite Type = TenantAdministrator
3. Add ProxyLibrary that add the TenantAdmin dll
4. Attach the Proxy to the existing Web Application
5. Enable SelfServiceCreation on the Web Application
6. IISReset

• Using the C# console create new site collections using the Tenant Admin API

PS Script

========

# The first section contains the variables you need to specify based on your needs

$webapp =  get-spwebapplication http://radimaging.co.uk:555 # My Web application (already exists)

$url = "http://radimaging.co.uk:555/sites/msotenantcontext" # Tenant Admin Site Collection used for provisioing (does not exist)
$WebsiteName = "Tenant Admin"
$WebsiteDesc = "Tenant Admin Site"
# better to use the site template "tenantadmin#0" using the team site site template "sts#0" causes
# an error msg (SubscriptionId can't be null), both work but you get less admin options # for provisioning.
$Template = "STS#0" 
$PrimaryLogin = "radimaging\psmith"
$PrimaryDisplay = "Paul smith"
$PrimaryEmail = paul.smith@radimaging.com
# Create a site collection and top level website
New-SPSite -Url $url -Name $WebsiteName –Description $WebsiteDesc -Template $Template -OwnerAlias $PrimaryLogin –OwnerEmail $PrimaryEmail
$web = Get-SPWeb $url
$web.CreateDefaultAssociatedGroups($web.site.owner,$web.site.secondaryowner,"")
$web.Dispose()

#Set the TenantAdmin SC
$site = get-spsite -Identity $url
$site.AdministrationSiteType = [Microsoft.SharePoint.SPAdministrationSiteType]::TenantAdministration
$newProxyLibrary = New-Object "Microsoft.SharePoint.Administration.SPClientCallableProxyLibrary"
$newProxyLibrary.AssemblyName = "Microsoft.Online.SharePoint.Dedicated.TenantAdmin.ServerStub, Version=15.0.0.0, Culture=neutral, PublicKeyToken=71e9bce111e9429c"
$newProxyLibrary.SupportAppAuthentication = $true
$webapp.ClientCallableSettings.ProxyLibraries.Add($newProxyLibrary)
$webapp.SelfServiceSiteCreationEnabled=$True
$webapp.Update()
Write-Host "Successfully added TenantAdmin ServerStub to ClientCallableProxyLibrary."
# Reset the memory of the web application
Write-Host "IISReset..."   
Restart-Service W3SVC,WAS -force
Write-Host "IISReset complete."

As always check out this post from Vesa Vuronen:

https://blogs.msdn.microsoft.com/vesku/2014/06/09/provisioning-site-collections-using-sp-app-model-in-on-premises-with-just-csom/