Add OAuth2 authentication (#147)

- Added Site settings > Authentication section
- Create/edit/delete your custom oauth2 configurations
- Login or signup with oauth2

app/javascript/constants/regex.ts

@@ -0,0 +1,2 @@
+export const EMAIL_REGEX = /(.+)@(.+){2,}\.(.+){2,}/;
+export const URL_REGEX = /^(ftp|http|https):\/\/[^ "]+$/;