Hello Mayur,
To confirm what you are seeing:
- Customer would login to SDM on a given browser and enter credentials.
- Customer is compelled to open a new tab on the same browser, then access the same SDM URL to open a second instance of SDM on that second tab.
- Expectation is that when the new tab is created and SDM accessed, no login prompt should be presented and end user would go in straightaway.
Assuming that is the case, this is not possible as each tab created for Service Desk constitutes its own session and login to be required. It is also a security violation since to allow for what you are describing, a given session would need to be allowed to be shared across multiple tabs, which can lead to an exploitable means to interfere and hijack an end user's session via browser spoofing.
The best solution I can think of that could be used to facilitate for a new browser tab not needing to enter credentials is to activate Single Sign On or Passthru Authentication.