Graph databases and authentication

I'm thinking about the high-level architecture for my next project and would like some advice.

The data will be composed of content captured from various sources, notes taken by users (each split up into n blocks & stored separately in the database!), metadata, and many cross-references between notes and parts of notes.

I'm under the impression that a Graph database would be best suited for this kind of system, as there will be many links between different pieces of information, and links will hold important metadata.

Do some of you have experience with Graph databases and authentication? What approach would you recommend?