Add question/answer-based CAPTCHA script (#3533)

* New captcha.sh question/answer based

* Keep original CAPTCHA script

Rather than replacing the original CAPTCHA script, keep it next to the
new one, for the moment.

* CAPTCHA-ng script cleanup

* remove various bashisms
* replace all echos with printf
+ add quotations to many variables

Co-authored-by: Adrien Bourmault <neox@os-k.eu>
Co-authored-by: nico wellpott <nico@magicbroccoli.de>

tools/captcha-ng.sh

@@ -0,0 +1,131 @@
+#!/bin/bash
+
+# Copyright © 2021 Adrien Bourmault (neox@os-k.eu)
+# This program is free software; you can redistribute it and/or modify
+# it under the terms of the GNU General Public License as published by
+# the Free Software Foundation; either version 2 of the License, or
+# (at your option) any later version.
+
+# This script is an example captcha script.
+# It takes the text to recognize in the captcha image as a parameter.
+# It return the image binary as a result. ejabberd support PNG, JPEG and GIF.
+
+# The whole idea of the captcha script is to let server admins adapt it to
+# their own needs. The goal is to be able to make the captcha generation as
+# unique as possible, to make the captcha challenge difficult to bypass by
+# a bot.
+# Server admins are thus supposed to write and use their own captcha generators.
+
+# This script relies on ImageMagick.
+# It is NOT compliant with ImageMagick forks like GraphicsMagick.
+
+INPUT=$1
+
+TRANSFORMATIONS=(INTRUDER SUM)
+DIGIT=(zero one two three four five six seven eight nine ten)
+
+if test -n "${BASH_VERSION:-''}" ; then
+    get_random ()
+    {  
+	R=$RANDOM
+    }
+else
+    for n in $(od -A n -t u2 -N 64 /dev/urandom); do RL="$RL$n "; done
+    get_random ()
+    {  
+	R=${RL%% *}
+	RL=${RL#* }
+    }
+fi
+
+INTRUDER()
+{
+NUMBERS=$(echo "$INPUT" | grep -o . | tr '\n' ' ')
+SORTED_UNIQ_NUM=$(echo "${NUMBERS[@]}" | sort -u | tr '\n' ' ')
+RANDOM_DIGITS=$(echo 123456789 | grep -o . | sort -R | tr '\n' ' ')
+INTRUDER=-1
+
+for i in $RANDOM_DIGITS
+do
+    if [[ ! " ${SORTED_UNIQ_NUM[@]} " =~ ${i} ]]; then
+        INTRUDER=$i
+        break
+    fi
+done
+
+# Worst case
+if [[ $INTRUDER -eq "-1" ]]
+then
+    printf "Type %s \n without changes" "$INPUT"
+    return
+fi
+
+for num in "${NUMBERS[@]}"
+do
+    get_random
+    R=$((R % 100))
+
+    if [[ $R -lt 60 ]]; then
+        NEWINPUT=${NEWINPUT}${num}${INTRUDER}
+    else
+        NEWINPUT=${NEWINPUT}${num}
+    fi
+done
+
+get_random
+R=$((R % 100))
+
+if [[ $R -lt 50 ]]; then
+    printf "Type %s by\n deleting the %s" "$NEWINPUT" "${DIGIT[$INTRUDER]}"
+else
+    printf "Enter %s by\n removing the %s" "$NEWINPUT" "${DIGIT[$INTRUDER]}"
+fi
+}
+
+
+SUM()
+{
+get_random
+RA=$((R % 100))
+
+if [[ $((INPUT % 2)) -eq 0 ]]; then
+    A=$((INPUT - RA))
+    B=$RA
+else
+    B=$((INPUT - RA))
+    A=$RA
+fi
+
+get_random
+R=$((R % 100))
+
+if [[ $R -lt 25 ]]; then
+    printf "Type the result\n of %s + %s" "$A" "$B"
+elif [[ $R -lt 50 ]]; then
+    printf "SUMx\n %s and %s" "$A" "$B"
+elif [[ $R -lt 75 ]]; then
+    printf "Add\n %s and %s" "$A" "$B"
+else
+    printf "Enter the result\n of %s + %s" "$A" "$B"
+fi
+}
+
+
+get_random
+
+RAND_ITALIC=$((R % 25))
+get_random
+
+RAND_ANGLE=$((R % 3))
+get_random
+
+RAND_INDEX=$((R % ${#TRANSFORMATIONS[@]}))
+
+convert -size 300x60 xc:none -pointsize 20 \
+\( -clone 0 -fill black \
+-stroke black -strokewidth 1 \
+-annotate "${RAND_ANGLE}x${RAND_ITALIC}+0+0" "\n $(${TRANSFORMATIONS[$RAND_INDEX]})" \
+-roll +"$ROLL_X"+0 \
+-wave "$WAVE1_AMPLITUDE"x"$WAVE1_LENGTH" \
+-roll -"$ROLL_X"+0 \) \
+-flatten -crop 300x60 +repage -quality 500 -depth 11 png:-