I need help building a cakephp 3.x LTI Tool Provider for Canvas LMS

I am a cakephp developer looking to build an interface from one of my projects to work within the Canvas LMS LTI consumer. I am confused about how this all works together. I understand how to add the tool to Canvas, I understand how to link to the tool in the Canvas modules. What I don't understand is how to get the tool to do the following. Check if the student coming from canvas is already in the database, if the student is in the database, then let them have access to their work, if not then register them as a new user with their data from Canvas. The data I need is the School, the Teacher, and themselves. If you can help me understand this concept or even have something already written that you can take me through a tutorial, then you are the right person for this job.