Simple implementation of Realm that reads an XML file to configure
the valid users, passwords, and roles. The file format (and default file
location) are identical to those currently supported by Tomcat 3.X.
IMPLEMENTATION NOTE: It is assumed that the in-memory
collection representing our defined users (and their roles) is initialized
at application startup and never modified again. Therefore, no thread
synchronization is performed around accesses to the principals collection.
IMPLEMENTATION NOTE: It is assumed that the in-memory collection representing our defined users (and their roles) is initialized at application startup and never modified again. Therefore, no thread synchronization is performed around accesses to the principals collection.