How to restrict unlogged/unauthorized users from viewing web pages in ASP.NET

I have some created web forms and I need to check whether the user is authenticated or not, before displaying the other web forms. All the users can access Default.aspx and About.aspx pages.
And I have three types of users namely- Admin,User and Super User. Also, I keep the authentication details in my own SQL server db.

How to freeze the header row in an Excel spreadsheet exported from ASP.NET

I’m exporting an ASP.NET gridview to Excel using the following function. The formatting is working really well, except I need to freeze the header row in Excel on the export. I’m really trying to avoid using a 3rd party Excel plugin for this, but unless there’s some archaic excel markup in my AddExcelStyling function.

Generate a unique id

I am a student at university and our task is to create a search engine. I am having difficulty generating a unique id to assign to each url when added into the frontier. I have attempted using the SHA-256 hashing algorithm as well as Guid. Here is the code that i used to implement the guid: