Transform a text string into an sha256 hash and then base64 encode it.

derive-username.sh

#!/bin/bash
#
# Takes in an e-mail address and answers back with the expected hash used
# for the AWS Cognito username field.
#

args=`getopt e: $*`
if [ $? != 0 ]; then
  echo "Usage: ..."
  exit 2
fi
set -- $args

for i
do
  case "$i"
  in
  -e)
    earg="$2"; shift;
    shift;;
  esac
done

if [ "X$earg" == "X" ]; then
  echo "Usage: ..."
  exit 3
else
  echo -n $earg | shasum -a 256 | cut -d " " -f 1 | xxd -r -p | base64
fi