Currently I\'m accessing JIRA API in C#.Net application with username and password. But I need to access the JIRA API without entering a username and a password even without has
Yes, JIRA supports OAuth for that purpose, see: https://developer.atlassian.com/display/JIRADEV/JIRA+REST+API+Example+-+OAuth+authentication
Unfortunately there's no C# sample code provided, but you should be able to assemble a solution from the other programming languages here: https://bitbucket.org/atlassian_tutorial/atlassian-oauth-examples/src
You should use a generic OAuth library anyhow.