How to use Session Id in ANT tool in Salesforce without username and password?

How to use Session Id in ANT tool in Salesforce without username and password?    

build.xml:        
    <target name="deploy">
        <sf:deploy
        sessionId="<SessionId>"
        serverurl="${sf.serverurl}"
        testLevel="RunLocalTests"
        deployroot="Retrieve"/>
    </target>