Firebase authentication with strings - firebase

Question

I am wondering if it's possible to do the firebase authentication on strings? I have seen it being done on keys like -XDhabsuduydvtest <- random test key.
Now i have this structure:
{
"conversations" : {
"person1" : {
"person2" : {
"0" : 0,
"last_read" : 1460377167535
}
},
"person2" : {
"person1" : {
"0" : 0,
"last_read" : 1460377125515
}
}
},
"messages" : {
"eb-uuid-729fc0ac-49b8-48fa-a2ff-f2ada67b9e4c-person1" : {
"body" : "Dit is een test vanuit iOS",
"date" : 1460383996536,
"sender" : "eb-uuid-729fc0ac-49b8-48fa-a2ff-f2ada67b9e4c"
},
"person1-person2" : {
"-KF49xHKqnDawywJ9H0b" : {
"body" : "test message",
"date" : 1460375639190,
"sender" : "person1"
},
"-KF4Fc1KHH31O4_l0QWh" : {
"body" : "new",
"date" : 1460377125013,
"sender" : "person2"
}
}
},
"users" : {
"eb-uuid-729fc0ac-49b8-48fa-a2ff-f2ada67b9e4c" : {
"chat_enabled" : true,
"email" : "test#gmail.com",
"first_name" : "John",
"last_name" : "Smith",
"provider" : "password",
"push_muted" : false,
"push_token" : "some-push-token",
"uid" : "729fc0ac-49b8-48fa-a2ff-f2ada67b9e4c",
"username" : "johnsmith"
},
"person1" : {
"first_name" : "person",
"last_name" : "one"
},
"person2" : {
"first_name" : "person",
"last_name" : "two"
}
}
}
plus some security rule i tried, obviously i'd like to check if the uuid's are the same, and not only if one exists
{
"rules": {
"messages": {
"$conv":{
//Person can only read a conversation he/she is participating in
".write": true,
".read": true,
".indexOn": ["date"]
}
},
"users":{
"$ebuuid":{
".write": "root.child('users').child($ebuuid).hasChild('uid')",
".read": "root.child('users').child($ebuuid).hasChild('uid')"
}
},
"conversations":{
".write": "data.child('uid').val() === auth.uid",
".read": true
}
}
}
(Replaced images with text)
I'm really not sure how to go from here now .. the user has some uid but i'm not sure how to check it with whether he or she can post messages etc ..