Belated greetings, Shawn:
I do not know of any specific guideline or rule that applies to breaking a long "nonsense" string of letters that is unspaced.
I suspect you already know that 14.7 of the Instruction Manual for Braille Transcribing – UEB Edition, 2015 says, " Make the division at a logical break and at a point that is not between two letters or between two digits." I acknowledge that isn't helpful in the case you describe.
First, I would double-check for any punctuation or words and endeavor to break between words or after any punctuation.
After checking that, if you still have to force a braille line break in a string of letters that is unspaced, I would endeavor to make the line break where it does not interrupt any contractions.
The braille user is lucky to have someone who is working hard to make even the messy web addresses be as reader-friendly as they can be.
Braille on!
–Kyle