(Lianja) 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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// 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.
loFac = createobject("CkFileAccess")
loXml = createobject("CkXml")

// 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>
// 

loDtExpire = createobject("CkDateTime")
loDtNow = createobject("CkDateTime")

lcFormDigestXmlFile = "qa_data/sharepoint/savedFormDigestValue.xml"
if (loFac.FileExists(lcFormDigestXmlFile) = .T.) then

    loXml.LoadXmlFile(lcFormDigestXmlFile)

    // Get the expire date/time
    loDtExpire.SetFromTimestamp(loXml.GetChildContent("d:ExpireDateTime"))

    // Get the current date/time
    loDtNow.SetFromCurrentSystemTime()

    // Get both times as Unix time values
    lnTNow = loDtNow.GetAsUnixTime(.F.)
    lnTExpire = loDtExpire.GetAsUnixTime(.F.)

    // If tNow >= tExpire, then fall through.
    // Otherwise, just use the cached digest value.
    if (lnTNow < lnTExpire) then
        ? "Cached digest value is not yet expired."
        ? "X-RequestDigest: " + loXml.GetChildContent("d:FormDigestValue")
        release loFac
        release loXml
        release loDtExpire
        release loDtNow
        return
    endif

endif

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

loHttp = createobject("CkHttp")

// If SharePoint Windows classic authentication is used, then set the 
// Login, Password, LoginDomain, and NtlmAuth properties.
loHttp.Login = "SHAREPOINT_USERNAME"
loHttp.Password = "SHAREPOINT_PASSWORD"
loHttp.LoginDomain = "SHAREPOINT_NTLM_DOMAIN"
loHttp.NtlmAuth = .T.

// 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.
lcSavedAccept = loHttp.Accept
loHttp.Accept = "application/xml"

// Note: The last argument ("utf-8") is meaningless here because the body is empty.
loResp = loHttp.PostXml("https://SHAREPOINT_HTTPS_DOMAIN/_api/contextinfo","","utf-8")
if (loHttp.LastMethodSuccess <> .T.) then
    ? loHttp.LastErrorText
    release loFac
    release loXml
    release loDtExpire
    release loDtNow
    release loHttp
    return
endif

// Restore the default Accept header
loHttp.Accept = lcSavedAccept

if (loResp.StatusCode <> 200) then
    // A response status code not equal to 200 indicates failure.
    ? "Response status code = " + str(loResp.StatusCode)
    ? "Response body:"
    ? loResp.BodyStr
    release loResp
    release loFac
    release loXml
    release loDtExpire
    release loDtNow
    release loHttp
    return
endif

loXml.LoadXml(loResp.BodyStr)
release loResp

// 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.
loXml2 = createobject("CkXml")

loXml2.Tag = "savedFormDigestValue"
loXml2.NewChild2("d:FormDigestValue",loXml.GetChildContent("d:FormDigestValue"))

lnTimeoutInSec = loXml.GetChildIntValue("d:FormDigestTimeoutSeconds")
? "Timeout in seconds = " + str(lnTimeoutInSec)

// Convert this to an expire timestamp.
// Let's make it expire 30 seconds prior to the actual timeout, just to be safe.
if (lnTimeoutInSec > 30) then
    lnTimeoutInSec = lnTimeoutInSec - 30
endif

loDtExpire.SetFromCurrentSystemTime()
loDtExpire.AddSeconds(lnTimeoutInSec)
loXml2.NewChild2("d:ExpireDateTime",loDtExpire.GetAsTimestamp(.F.))

// Persist the digest and expire time to a file.
loXml2.SaveXml(lcFormDigestXmlFile)

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


release loFac
release loXml
release loDtExpire
release loDtNow
release loHttp
release loXml2