SharePoint Online - Update User Profile Properties Using CSOM App

I have a console application where I update the properties of a SharePoint Online user profile via CSOM. When I do it with the following code below (using username and password) it works fine.

private static void UpdateUserProfileProperties()
{
    var userAccountName = "i:0#.f|membership|myAccounName@mySite.com";
    var siteUrl = "https://mySite-admin.sharepoint.com";
    var myUserName = "myUserName";
    var myPassword = "myPassword";
    var secureStringPassword = new SecureString();
    myPassword.ToList().ForEach(c => secureStringPassword.AppendChar(c));

    using (var context = new ClientContext(siteUrl))
    {
        var credentials = new SharePointOnlineCredentials(myUserName, secureStringPassword);
        context.Credentials = credentials;

        var peopleManager = new PeopleManager(context);
        var personProperties = peopleManager.GetPropertiesFor(userAccountName);

        context.Load(personProperties, p => p.AccountName, p => p.UserProfileProperties);
        context.ExecuteQuery();
    }
}

      

        
        
        
      

    

I have now created an application in SharePoint (using the AppRegNew.aspx page). I have granted permissions at the app tenant level (via the AppInv.aspx page) and the following XML permission request:

<AppPermissionRequests AllowAppOnlyPolicy="true">
    <AppPermissionRequest Scope="http://sharepoint/content/tenant" Right="FullControl"/>
</AppPermissionRequests>

      

        
        
        
      

    

Now I am using clientID / clientSecret for authentication instead of username and password - using this code:

public static void UpdateUserProfileProperties2()
{
    var userAccountName = "i:0#.f|membership|myAccounName@mySite.com";
    var siteUrl = "https://mySite-admin.sharepoint.com";
    var siteUri = new Uri(siteUrl);
    var siteRealm = TokenHelper.GetRealmFromTargetUrl(siteUri);
    var siteToken = TokenHelper.GetAppOnlyAccessToken(TokenHelper.SharePointPrincipal, siteUri.Authority, siteRealm).AccessToken;

    using (var context = TokenHelper.GetClientContextWithAccessToken(siteUri.ToString(), siteToken))
    {
        var peopleManager = new PeopleManager(context);
        var personProperties = peopleManager.GetPropertiesFor(userAccountName);

        context.Load(personProperties, p => p.AccountName, p => p.UserProfileProperties);
        context.ExecuteQuery();
    }
}

      

        
        
        
      

    

I can get the token and context just fine. When the line is executed context.ExecuteQuery();

, I get the following exception:

Microsoft.SharePoint.Client.ServerUnauthorizedAccessException: Access is denied. You do not have permission to perform this action or access this resource.

The clientID / clientSecret of the application works for all kinds of other operations on the site. Is it possible to upload custom properties to admin site using clientID / clientSecret? If so, can you provide an example? How can I grant the application the appropriate permissions?