#include <StringConstants.au3> ; to declare the Constants of StringRegExp
#include <Array.au3> ; UDF needed for _ArrayDisplay and _ArrayConcatenate
Local $sRegex = "\[INFO\] \[(\S+):\d+\S+\] Authentication failed with user: '(\S*)'.$"
Local $sString = "2015-12-02 23:17:35.845 [INFO] [IP.ADD.RE.SS:50364:HTTP2-7] Authentication failed with user: 'username'."
Local $aArray = StringRegExp($sString, $sRegex, $STR_REGEXPARRAYFULLMATCH)
; Present the entire match result
_ArrayDisplay($aArray, "Result")
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for AutoIt, please visit: https://www.autoitscript.com/autoit3/docs/functions/StringRegExp.htm