Notice anything repeating in some kind of way?
Looks like the string is repeated twice but reversed. Split it into two parts
Now looking at the first part, you can see the passcode format
The fact the the string repeats itself reversed is a mirror effect. Mirror is a valid keyword.
All letters, you can see a few numbers in reverse.
Not sure how to explain that one but here’s how I got it. Seeing those in, ht, ie & es could mean reversed numbers.
Reverse the whole string
Split where you see numbers
se ei th oztainenabranqyt th ni
The passcode format is LLL## keyword ###LL. We have 3 numbers at the start so we can assume oz here the letters for the suffix. Same for the prefix, qyt are right before the 2 last numbers.
se ei th oz tainenabran qyt th ni
We now have
783oz tainenabran qyt39
Searching for taineabran on google gives a link to a character of Memory Alpha namen Tain Enabran who was head of the Obsidian order. Obsidian is a valid keyword
Looks like all the ingredients are there.
You could do a 4×4 grid and read the rows in this order 2, 3 & 1 or you can simply start reading at the T to get