Using the Podio API with PowerShell (Authentification, Getting Items from an app). We are pretending that the podio app, that we want to access, stores a list of people and we want to retrieve the first- and last names

Get-PodioAPI.ps1

function Get-PodioAPIAuthorization() {

    $PostParams = @{grant_type = "app"; app_id = ""; app_token = ""; client_id = ""; redirect_uri = ""; client_secret = ""}
    #Params for the Authentification have to be hardcoded

    $Result = Invoke-RestMethod -Uri https://podio.com/oauth/token -Method POST -Body $postParams  

    return $Result.access_token 

}

function Get-PodioApiAppItems($AccessToken) {
    #The Access token will be set in the header of the post request
  
    $HeaderParams = @{Authorization = "Bearer " + $AccessToken}

    $PostParams = @{limit = 500} | ConvertTo-Json
    #This API needs the postparams as JSON Object"

    $Result = Invoke-RestMethod -Uri https://api.podio.com/item/app/xxxxxxxx/filter/ -Method POST -Headers $HeaderParams -Body $postParams -ContentType "application/json" 

    $Result = $Result.items 
    #The actual app items are stored in $result.items. Instead of working with Select-Object -ExpandProperty items, this allows for debugging.
        
    $AppItems = New-Object System.Collections.Generic.List[System.Object]

    foreach ($item in $Result) {
        
        #Process every item
        
        #Parse Attributes and store them in temporary variables 

        $id = $item.app_item_id_formatted
        $FirstName = $item.fields | Where-Object {$_.label -like "FirstName"} | Select-Object -ExpandProperty Values | Select-Object -ExpandProperty Value
        $LastName = $item.fields | Where-Object {$_.label -like "LastName"} | Select-Object -ExpandProperty Values | Select-Object -ExpandProperty Value

        # Build a custom object and store it in the AppItems List.
        $AppItems.Add([PSCustomObject]@{PSTypeName = "Item"; ID = $id; FirstName = $FirstName; LastName = $LastName})
    }

    return $AppItems  

}

Get-PodioApiAppItems(Get-PodioAPIAuthorization)