run.ps1

using namespace System.Net

# Input bindings are passed in via param block.
param($Request, $TriggerMetadata)

$APIName = $TriggerMetadata.FunctionName
Write-LogMessage -user $request.headers.'x-ms-client-principal' -API $APINAME  -message "Accessed this API" -Sev "Debug"


# Write to the Azure Functions log stream.
Write-Host "PowerShell HTTP trigger function processed a request."

# Interact with query parameters or the body of the request.
$tenantfilter = $Request.Query.TenantFilter
$appFilter = $Request.Query.ID
$AssignTo = $Request.Query.AssignTo
$AssignBody = switch ($AssignTo) {

    'AllUsers' {
        @"
{"mobileAppAssignments":[{"@odata.type":"#microsoft.graph.mobileAppAssignment","target":{"@odata.type":"#microsoft.graph.allLicensedUsersAssignmentTarget"},"intent":"Required","settings":null}]}
"@ 
    }

    'AllDevices' {
        @"
{"mobileAppAssignments":[{"@odata.type":"#microsoft.graph.mobileAppAssignment","target":{"@odata.type":"#microsoft.graph.allDevicesAssignmentTarget"},"intent":"Required","settings":null}]}
"@
    }

    'Both' {
        @"
{"mobileAppAssignments":[{"@odata.type":"#microsoft.graph.mobileAppAssignment","target":{"@odata.type":"#microsoft.graph.allLicensedUsersAssignmentTarget"},"intent":"Required","settings":null},{"@odata.type":"#microsoft.graph.mobileAppAssignment","target":{"@odata.type":"#microsoft.graph.allDevicesAssignmentTarget"},"intent":"Required","settings":null}]}
"@
    }

}
$body = [pscustomobject]@{"Results" = "$($TenantFilter): Assigned app to $assignTo" }
try {
    $GraphRequest = New-Graphpostrequest -uri "https://graph.microsoft.com/beta/deviceAppManagement/mobileApps/$appFilter/assign" -tenantid $TenantFilter -body $Assignbody
    Write-LogMessage -user $request.headers.'x-ms-client-principal' -API $APINAME -tenant $($tenantfilter) -message "Assigned $($appFilter) to $assignTo" -Sev "Info"

}
catch {
    Write-LogMessage -user $request.headers.'x-ms-client-principal' -API $APINAME -tenant $($tenantfilter) -message "Failed to assign app $($appFilter): $($_.Exception.Message)" -Sev "Error"
    $body = [pscustomobject]@{"Results" = "Failed to assign. $($_.Exception.Message)" }
}

# Associate values to output bindings by calling 'Push-OutputBinding'.
Push-OutputBinding -Name Response -Value ([HttpResponseContext]@{
        StatusCode = [HttpStatusCode]::OK
        Body       = $body
    })