well not quite that fast and easy -- when you get a key with two colors that matches the door, you can use it and get it. Otherwise, people can help you enter, if there is a party or other social event... It will come along...
Plexus has two entrances, one in Firdaus Finds, the other in Kanji Sink. You can search for either of those streets on the map search.
The Kanji Sink door is much easier to get the key for, as that key spawns quite quickly.
As larky said, it really is as easy as Firestone made it sound.