(PowerShell) SharePoint -- Get Server Form Digest Value

Demonstrates how to get a server form digest value to be placed in the X-RequestDigest HTTP request header for POST, PUT, MERGE, and DELETE requests. A form digest value is typically valid for 1800 seconds (i.e. 30 minutes). This example persists the value to a file, and only requests a new form digest value if the existing one is near expiration.

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Add-Type -Path "C:\chilkat\ChilkatDotNet47-9.5.0-x64\ChilkatDotNet47.dll"

# This requires the Chilkat API to have been previously unlocked.
# See Global Unlock Sample for sample code.

# First, let's see if we already have a persisted form digest value
# that hasn't yet expired.
$fac = New-Object Chilkat.FileAccess
$xml = New-Object Chilkat.Xml

# My example code (below) persists the form digest XML in this format:
# 
# 	<savedFormDigestValue>
# 	<d:ExpireDateTime>2017-04-12T20:46:39Z</d:ExpireDateTime>
# 	<d:FormDigestValue>0x3059FFB920651834540F3E6792EA73F5746B302E953FF4E808E485DB1E6C2836C7CF924644995F092453B02A94DE14A7962674B7B16780AF16EAFB8C246BCDC7,12 Apr 2017 17:08:22 -0000</d:FormDigestValue>
# 	</savedFormDigestValue>
# 

$dtExpire = New-Object Chilkat.CkDateTime
$dtNow = New-Object Chilkat.CkDateTime

$formDigestXmlFile = "qa_data/sharepoint/savedFormDigestValue.xml"
if ($fac.FileExists($formDigestXmlFile) -eq $true) {

    $xml.LoadXmlFile($formDigestXmlFile)

    # Get the expire date/time
    $dtExpire.SetFromTimestamp($xml.GetChildContent("d:ExpireDateTime"))

    # Get the current date/time
    $dtNow.SetFromCurrentSystemTime()

    # Get both times as Unix time values
    $tNow = $dtNow.GetAsUnixTime($false)
    $tExpire = $dtExpire.GetAsUnixTime($false)

    # If tNow >= tExpire, then fall through.
    # Otherwise, just use the cached digest value.
    if ($tNow -lt $tExpire) {
        $("Cached digest value is not yet expired.")
        $("X-RequestDigest: " + $xml.GetChildContent("d:FormDigestValue"))
        exit
    }

}

# If we got to this point, the cached digest value either does not exist, or expired.

$http = New-Object Chilkat.Http

# If SharePoint Windows classic authentication is used, then set the 
# Login, Password, LoginDomain, and NtlmAuth properties.
$http.Login = "SHAREPOINT_USERNAME"
$http.Password = "SHAREPOINT_PASSWORD"
$http.LoginDomain = "SHAREPOINT_NTLM_DOMAIN"
$http.NtlmAuth = $true

# The more common case is to use SharePoint Online authentication (via the SPOIDCRL cookie).
# If so, do not set Login, Password, LoginDomain, and NtlmAuth, and instead
# establish the cookie as shown at SharePoint Online Authentication

# When creating, updating, and deleting SharePoint entities, we'll need
# to first get the server's form digest value to send in the X-RequestDigest header.
# This can be retrieved by making a POST request with an empty body to
# http://<site url>/_api/contextinfo and extracting the value of the
# d:FormDigestValue node in the XML that the contextinfo endpoint returns.

# Apparently, SharePoint needs an "Accept" request header equal to "application/xml",
# otherwise SharePoint will return an utterly incomprehensible and useless error message.
$savedAccept = $http.Accept
$http.Accept = "application/xml"

# Note: The last argument ("utf-8") is meaningless here because the body is empty.
$resp = $http.PostXml("https://SHAREPOINT_HTTPS_DOMAIN/_api/contextinfo","","utf-8")
if ($http.LastMethodSuccess -ne $true) {
    $($http.LastErrorText)
    exit
}

# Restore the default Accept header
$http.Accept = $savedAccept

if ($resp.StatusCode -ne 200) {
    # A response status code not equal to 200 indicates failure.
    $("Response status code = " + $resp.StatusCode)
    $("Response body:")
    $($resp.BodyStr)

    exit
}

$xml.LoadXml($resp.BodyStr)

# The response XML looks like this:

# <?xml version="1.0" encoding="utf-8" ?>
# <d:GetContextWebInformation xmlns:d="http://schemas.microsoft.com/ado/2007/08/dataservices" xmlns:m="http://schemas.microsoft.com/ado/2007/08/dataservices/metadata" xmlns:georss="http://www.georss.org/georss" xmlns:gml="http://www.opengis.net/gml" m:type="SP.ContextWebInformation">
#     <d:FormDigestTimeoutSeconds m:type="Edm.Int32">1800</d:FormDigestTimeoutSeconds>
#     <d:FormDigestValue>0x3059FFB920651834540F3E6792EA73F5746B302E953FF4E808E485DB1E6C2836C7CF924644995F092453B02A94DE14A7962674B7B16780AF16EAFB8C246BCDC7,12 Apr 2017 17:08:22 -0000</d:FormDigestValue>
#     <d:LibraryVersion>15.0.4569.1000</d:LibraryVersion>
#     <d:SiteFullUrl>https://SHAREPOINT_HTTPS_DOMAIN</d:SiteFullUrl>
#     <d:SupportedSchemaVersions m:type="Collection(Edm.String)">
#         <d:element>14.0.0.0</d:element>
#         <d:element>15.0.0.0</d:element>
#     </d:SupportedSchemaVersions>
#     <d:WebFullUrl>https://SHAREPOINT_HTTPS_DOMAIN</d:WebFullUrl>
# </d:GetContextWebInformation>
# 

# Cache the digest value, and also an expiration time.  If this code is run again
# before the digest expires, we'll just get it from the file.
$xml2 = New-Object Chilkat.Xml

$xml2.Tag = "savedFormDigestValue"
$xml2.NewChild2("d:FormDigestValue",$xml.GetChildContent("d:FormDigestValue"))

$timeoutInSec = $xml.GetChildIntValue("d:FormDigestTimeoutSeconds")
$("Timeout in seconds = " + $timeoutInSec)

# Convert this to an expire timestamp.
# Let's make it expire 30 seconds prior to the actual timeout, just to be safe.
if ($timeoutInSec -gt 30) {
    $timeoutInSec = $timeoutInSec - 30
}

$dtExpire.SetFromCurrentSystemTime()
$dtExpire.AddSeconds($timeoutInSec)
$xml2.NewChild2("d:ExpireDateTime",$dtExpire.GetAsTimestamp($false))

# Persist the digest and expire time to a file.
$xml2.SaveXml($formDigestXmlFile)

$("Here is the new form digest value:")
$("X-RequestDigest: " + $xml.GetChildContent("d:FormDigestValue"))