Since you did not post the code you have so we can integrate a solution into it, here is more complete solution.
Code:
break on
$LineNum = 0
$File = 'C:\file.txt'
$Array = ReadFile($file)
For each $Line in $Array
 If Instr($Line,'Authorization ID')
  'Found on line # ' $LineNum ?
  $AuthID = Trim(Split($Array[$LineNum],'=')[0])
  $AuthID ?
 EndIf
 $LineNum = $LineNum + 1
Next

;Function ReadFile() 
;Author Radimus 
;Contributors Lonky... This is basically his code that I trimmed down to its 
; simplest function 
;Action Reads a file into an array 
; http://www.kixtart.org/ubbthreads/showflat.php?Cat=&Number=83675 

Function ReadFile($file) 
Dim $lf, $f, $_, $t 
$lf=Chr(10) 
$f=FreeFileHandle 
$_=Open($f,$file) 
If @ERROR Exit @ERROR EndIf 
Do $t=$t+$lf+ReadLine($f) Until @ERROR 
$_=Close($f) 
$ReadFile=Split(SubStr($t,2),$lf) 
EndFunction
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