public void addStringPermission(String permission) {
        if (this.stringPermissions == null) {
            this.stringPermissions = new HashSet<String>();
        }
        this.stringPermissions.add(permission);
    }
Adds (assigns) a permission to those directly associated with the account.  If the account doesn't yet have any
direct permissions, a new permission collection (a Set&lt;String&gt;) will be created automatically.

@param permission the permission to add to those directly assigned to the account.
core/src/main/java/org/apache/shiro/authz/SimpleAuthorizationInfo.java