I seem to be stuck with the following:
I got a webforms application (.net4) with a forms authentication
<sessionState mode="InProc" cookieless="false" timeout="130" />
<authentication mode="Forms">
<forms name=".ASPXAUTH" loginUrl="login.aspx" defaultUrl="/"
protection="All" timeout="20160" path="/" requireSSL="false" slidingExpiration="true"
cookieless="UseCookies" domain="" >
</forms>
</authentication>
<machineKey validationKey="..." decryptionKey="..." validation="SHA1" decryption="AES" />
and a login form with a login control
<asp:Login ID="ctlLogin" runat="server" DisplayRememberMe="False" RememberMeSet="true ...
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