static ApplicationId getFromApplicationId(HttpRequest request) {
        String from = request.getProperty("from");
        if (from == null || "".equals(from))
            throw new BadRequestException("Parameter 'from' has illegal value '" + from + "'");

        return getAndValidateFromParameter(URI.create(from));
    }
A handler that is able to create a session from an application package,
or create a new session from a previous session (with id or the "active" session).
Handles /application/v2/ requests

@author hmusum
configserver/src/main/java/com/yahoo/vespa/config/server/http/v2/SessionCreateHandler.java