I’ll break it down into the components you could use.
To detect a player coming up to a door you can use a trigger actor. Use the OnBeginOverlap event to call e.g. the AskForCode function.
To display ‘please insert code’ you could add a TextRender Component or a UMG widget(either hud or 3d widget) with a ‘please insert code’ Text and a TextBox for input to your door blueprint and have it initially hidden. When your AskForCode function gets called, change your widget to visible and pass in a reference to your door blueprint actor into the widget blueprint for later and once it is visible focus the input to the widget.
Now just override the umg widget TextBox OnTextChanged or submitted to check the typed text, it it matches, call an OpenDoor function (animate/unblock to your liking) on the door blueprint you passed in as reference into the widget earlier.