Access Graph API from Acumatica login by SharePoint user

Hi, I am using Acumatica 25R1enabled with SSO, so SharePoint user can able to login in Acumatica by click on ‘Active directory‘ on login screen and put their SSO credential. 

I am trying from my Acumatica Instance to call Graph API to get data from SharePoint of login user but not find any way to do.

In the this code I can get the loin user name, but I am not able to get the access token of graph API to get data, please check this code and help me what I am missing

var httpContext = HttpContext.Current;

if(httpContext != null && httpContext.User.Identity.IsAuthenticated) {

ClaimsPrincipal user = httpContext.User as ClaimsPrincipal;

var accessTokenClaim = user?.FindFirst("access_token");

                // Ensure this claim exists

                if(accessTokenClaim != null) {

                    return accessTokenClaim.Value; // Return the access token if it exists

                }

}

Regards,

Abhishek