php - possible characters base64 url safe function

Question

What is the range of possible characters returned from this string?

function base64url_encode($data) 
{ 
  return rtrim(strtr(base64_encode($data), '+/', '-_'), '='); 
} 

My guess is [a-z0-9-_]

Answer 1

Base64 encoded strings may contain the characters a-z A-Z 0-9 + / =.

You're removing the right-padding = and replacing + with - and / with _.

So in your case, the possible characters are a-z A-Z 0-9 - _

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