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Java framework for authenticating LTI launch requests from the Canvas LMS

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package edu.ksu.lti.launch.service;

import edu.ksu.lti.launch.exception.NoLtiSessionException;
import edu.ksu.lti.launch.model.LtiSession;
import org.springframework.stereotype.Service;
import org.springframework.web.context.request.RequestContextHolder;
import org.springframework.web.context.request.ServletRequestAttributes;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpSession;

/**
 * Created by alexanda on 7/27/16.
 */
@Service
public class LtiSessionService {

    /**
     * Get the LtiSession object from the HTTP session. It is put there up in the ltiLaunch method.
     * This should really be done using a SpringSecurityContext to get the authenticated principal
     * which could then hold this LTI information. But I'm having serious trouble figuring out how to
     * do this correctly and I need *some* kind of session management for right now.
     * Another approach would be to create this as a session scoped bean but the problem there is that
     * I need to share this session object across controllers (the OauthController to be specific) and
     * this breaks for some reason so I'm rolling my own session management here.
     *
     * @return The current user's LTI session information
     * @throws edu.ksu.lti.launch.exception.NoLtiSessionException if the user does not have a valid LTI session.
     */
    public LtiSession getLtiSession() throws NoLtiSessionException {
        ServletRequestAttributes sra = (ServletRequestAttributes) RequestContextHolder.getRequestAttributes();
        HttpServletRequest req = sra.getRequest();
        HttpSession session = req.getSession();
        LtiSession ltiSession = (LtiSession) session.getAttribute(LtiSession.class.getName());
        if (ltiSession == null) {
            throw new NoLtiSessionException();
        }
        return ltiSession;
    }
}