The Rift Portal is a portal that has a slight chance of appearing in any world, it leads the player to the lore world. There the player can see many different things inside.
The password in the 
Password Portal inside the world you are guided to is still unknown there is a person named "-F" that has been revealed to every secret item in the game but we still dont know anything about him (item like the 
Sign next to the 
Flaming Shard in the Netherworld).
Items found (as of April 7, 2020)
These are some items found inside the Rift Portal.
Videos
Here is one video that took some information as much as possible.
Youtube Link
{Every youtube link that has someone going inside the rift will be added soon because as i say , more evidence = more informationhttps://youtu.be/aQzgHAZwg34