This was a great source that I have used to build a std API interface to use. I have extended this by including the data download, validation, cleanup and upload all together. I have written a post about what I have done here: ETBMA R12 Case Study - Powershell and the Apptio API's  

Bear in mind per the Browser Security Protocol Update blog post Apptio has discontinued support for TLS v1.0 and TLS v1.1 so you need PowerShell to be using TLS 1.2 or higher.  The ServicePointManager.SecurityProtocol Property (System.Net) | Microsoft Docs document describes the utility used to specify TLS version. Command line usage would look like this:

PS> [Net.ServicePointManager]::SecurityProtocol = [Net.SecurityProtocolType]::Tls12
PS> Invoke-WebRequest "https://client.apptio.com...

Scripts may need to utilize this if it isn't the default in your environment.

Super helpful. Thank you.

Excellent supplement Robert!

Thought I would share my code, maybe it can help another with strict security requirements! 

I wrote a PowerShell .ps1 for authenticating via FrontDoor for API calls.  You must authenticate via API.  For my scripts I am using a Windows 2012 R2 server with windows task scheduler.  Couple things to keep in mind.

1. You can setup a secured API key if your environment utilizes SSO, this is done through the user account management in Frontdoor.

2. I masked the API key on our server and encrypted it due to security reasons

3. Use at your own risk

4. I would suggest coping and pasting the below into PowerShell ISE for a better view of the code

This script is pretty long and if you have any specific questions please let me know!

#############################################################################################################

#Script to use API calls for Apptio FrontDoor applications #
#Script written by Robert Schneider December 15th 2017 currently using API Key #
#############################################################################################################

$PSScriptRoot = Split-Path $MyInvocation.MyCommand.Path -Parent #set the current path of the script Get-location |select path 
$secretkey = "$PSScriptRoot\secretkey.pwd" #setting path of secretkey file
$publickey = "$PSScriptRoot\publickey.pwd" #setting path of publickey file

if (((Test-Path $secretkey) -eq $false) -or (Test-Path $publickey) -eq $false){ #testing path for public / secret key file

#below is a custom input form for the public/private key pair
Add-Type -AssemblyName System.Windows.Forms
Add-Type -AssemblyName System.Drawing

$objForm = New-Object System.Windows.Forms.Form 
$objForm.Text = "Public/Private Key Entry"
$objForm.Size = New-Object System.Drawing.Size(300,250) 
$objForm.StartPosition = "CenterScreen"

$OKButton = New-Object System.Windows.Forms.Button
$OKButton.Location = New-Object System.Drawing.Size(75,180)
$OKButton.Size = New-Object System.Drawing.Size(75,23)
$OKButton.Text = "OK"
$OKButton.DialogResult = [System.windows.forms.dialogresult]::OK
$objForm.AcceptButton= $OKButton
$objForm.Controls.Add($OKButton)

$CancelButton = New-Object System.Windows.Forms.Button
$CancelButton.Location = New-Object System.Drawing.Size(150,180)
$CancelButton.Size = New-Object System.Drawing.Size(75,23)
$CancelButton.Text = "Cancel"
$CancelButton.DialogResult = [System.windows.forms.dialogresult]::Cancel
$objForm.AcceptButton= $CancelButton
$objForm.Controls.Add($CancelButton)

$objLabel = New-Object System.Windows.Forms.Label
$objLabel.Location = New-Object System.Drawing.Size(10,20) 
$objLabel.Size = New-Object System.Drawing.Size(280,20) 
$objLabel.Text = "PLEASE ENTER PUBLIC KEY:"
$objForm.Controls.Add($objLabel)

$objTextBox = New-Object System.Windows.Forms.TextBox 
$objTextBox.Location = New-Object System.Drawing.Size(10,40) 
$objTextBox.Size = New-Object System.Drawing.Size(260,20) 
$objForm.Controls.Add($objTextBox)

$objLabel = New-Object System.Windows.Forms.Label
$objLabel.Location = New-Object System.Drawing.Size(10,100) 
$objLabel.Size = New-Object System.Drawing.Size(280,20) 
$objLabel.Text = "PLEASE ENTER PRIVATE KEY:"
$objForm.Controls.Add($objLabel)

$objTextBox2 = New-Object System.Windows.Forms.TextBox 
$objTextBox2.Location = New-Object System.Drawing.Size(10,120) 
$objTextBox2.Size = New-Object System.Drawing.Size(260,20) 
$objForm.Controls.Add($objTextBox2)

$objForm.topmost = $true

$result = $objform.ShowDialog()

if ($result -eq [System.Windows.Forms.DialogResult]::OK)
{
$x= $objTextBox.Text
$y= $objTextBox2.Text
}
if ($result -eq [System.Windows.Forms.DialogResult]::Cancel)
{
$wshell = New-Object -ComObject Wscript.Shell
$wshell.Popup("YOU HAVE CANCELLED YOUR INPUT, PLEASE TRY AGAIN AND ENSURE YOU'RE SELECTING OK.",0,"Error")|Out-Null
exit}

#end of custom input form for the public/private key pair

$x|ConvertTo-SecureString -AsPlainText -Force|convertFrom-SecureString > $publickey #exporting and encrypting publickey
$y|ConvertTo-SecureString -AsPlainText -Force|convertFrom-SecureString > $secretkey #exporting and encrypting secretkey
}

$secretkeyplain = Get-Content -path $secretkey #pulling encrypted secretkey

$publickeyplain = Get-Content -path $publickey #pulling encrypted publickey

$PlainTextSecret= [Runtime.InteropServices.Marshal]::PtrToStringAuto([Runtime.InteropServices.Marshal]::SecureStringToBSTR( (ConvertTo-SecureString $secretkeyplain) )) #unencrypting secretkey

$PlainTextPublic= [Runtime.InteropServices.Marshal]::PtrToStringAuto([Runtime.InteropServices.Marshal]::SecureStringToBSTR( (ConvertTo-SecureString $publickeyplain) ))#unencrypting publickey

$string =@{keySecret=$PlainTextSecret;keyAccess=$PlainTextPublic} |convertto-json -compress #creating hash-table to pass public/private key pair to apptio

$header = Invoke-WebRequest -Method Post -Uri 'https://frontdoor.apptio.com/service/apikeylogin' -ContentType "application/json" -Body $string |Select -ExpandProperty headers #retrieving key header for opentoken

$opentoken=@{"apptio-opentoken"=$header."apptio-opentoken"} #must be in a table format for passing credentials must pass in -header parameter in invoke-restmethod (get) and Invoke-WebRequest (curl/post)

#############################################################################################################
#Remaining script are API calls using opentoken from authentication above must pass $opentoken in -header #
#############################################################################################################

Thanks Dan, that worked!

The following should work when appended:

&showRawNumbers=true&rawNumberPrecision=15

Is there a download argument that will pull the decimal places of a value? When exporting to excel I can see the decimal places of the data, but when pulled via API it is being rounded to a whole number. Thanks!