Set the trust-auth-realm-ref property in the sun-sip.xml file. This property refers to the jdbcRealm that has assertedRealm as its JAAS context value. See Configuring a Realm for Identity Authentication.
For example:
<sun-sip-app>
...
<property name="trust-auth-realm-ref" value="MyAssertedAppRealm" />
</sun-sip-app>