OWA Direct Access with out Login page

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SSO

ISS

LDAP

I create a i-frame widget of the Outlook Web Access.Now I want is That-
When the User Write the URL of the Web page on Which a Outlook widget is placed then it shows log in page in the Widget.now i want that When Widget i-frame loaded it automatically authenticated the Active Directory's user(automatically logged in) to access there Outlook mail Account.
Something like Single Sign on.
How can i achieved this?
Thank You.