I have discussed with Ronald Monzillo about the run-as in servlet.
I try to summarize his comments as follows:
a) In "A.8 Changes Since Servlet 2.3", it states
Clarification: "run-as" identity must apply to all calls from a servlet including init() and destroy() (12.7)
There is no such clarification in the section 12.7 or in the security chapter, so the clarification may have been lost, but the appendix clearly notes the intent, and thus he thinks it is required that a specified run-as identity be in effect during init() and destroy().
b) Note that section 15.3.1 Propagation of Security Identity in EJB Calls, requires that propagation occur whenever an ejb is called by a servlet (without consideration of the Servlet method form which the ejb call is made). That may be going too far, but it would at least support that run-as should be honored within init(); where it is has become common practice to invoke ejbs, and where (unlike the case of calls to ejbs from servlet context listeners), there is a mapping to a specific servlet on which to look for a run-as specification.
I think we should only propagate the security identity when Servlet#init, Servlet#destroy and Servlet#service are called.
(So, there will be no security identity propagation for Servlet#getServletConfig, Servlet#getServletInfo.)