otp: added a plugin for oathtool one-time passwords (#3862)

plugins/otp/otp.plugin.zsh

+export OTP_HOME=~/.otp
+mkdir -p $OTP_HOME
+
+function ot () {
+  if ! command -v oathtool > /dev/null 2>&1; then
+    echo "Note: you need to install oathtool or oath-toolkit, depending on your OS or distribution."
+    return 1
+  fi
+
+  if ! command -v gpg > /dev/null 2>&1; then
+    echo "Note: you need to install gpg and create an ID using 'gpg --gen-key', unless you have one already."
+    return 1
+  fi
+
+  if [[ `uname` == 'Darwin' ]] then # MacOS X
+    export COPY_CMD='pbcopy'
+  elif command -v xsel > /dev/null 2>&1; then # Any Unix with xsel installed
+    export COPY_CMD='xsel --clipboard --input'
+  else
+    COPY_CMD='true'
+  fi
+
+  if [[ "x$1" == "x" ]]; then
+    echo "usage: otpw <profile.name>"
+    return 1
+  elif [ ! -f $OTP_HOME/$1.otp.asc ]; then
+    echo "missing profile $1, you might need to create it first using otp_add_device"
+    return 1
+  else
+    totpkey=$(gpg --decrypt $OTP_HOME/$1.otp.asc)
+    oathtool --totp --b $totpkey | tee /dev/stderr | `echo $COPY_CMD`
+    if [[ $COPY_CMD == 'true' ]] then
+      echo "Note: you might consider installing xsel for clipboard integration"
+    fi
+  fi
+}
+
+function otp_add_device () {
+  if [[ "x$1" == "x" ]] then
+    echo "usage: otp_add <profile.name>"
+    return 1
+  else
+    echo "Enter an email address attached to your GPG private key, then paste the secret configuration key followed by ^D"
+
+    rm -f $OTP_HOME/$1.otp.asc
+    gpg --armor --encrypt --output $OTP_HOME/$1.otp.asc /dev/stdin
+  fi
+}
+
+function otp_devices () {
+  reply=($(find $OTP_HOME -name \*.otp.asc | xargs basename -s .otp.asc))
+}
+
+compctl -K otp_devices ot