property 'auth' does not exist on type 'angularfireauth' angular
1 - npm uninstall firebase @angular/fire
2- package.json
3 - dependencies { ... "@angular/fire": "6.0.0", "firebase": "7.14.1", ... }
4 - change
dependencies { ... "@angular/fire": "^5.4.2",
...
5 - save
6 - npm install firebase @angular/fire
if you find another much better solution but for now this worked