scripts/jwtdec.sh

#!/bin/sh

# jwtdec.sh -j [JWT_enc]
# jwtdec.sh -j [JWT_enc] -h [HEADER_dec] -p [PAYLOAD_dec]

for arg in "$@"
do
    case $arg in
        --hh) echo "Usage: jwtdec.sh -j [JWT_enc] -h [HEADER_dec] -p [PAYLOAD_dec]"; exit 0 ;;
        -j|--jwt) jwt=$2; shift;shift ;;
        -h|--header) header_supp=$2; shift;shift ;;
        -p|--payload) payload_supp=$2; shift;shift ;;
    esac
done

echo "Decoding from -j"
echo "$jwt"
header=$(echo "$jwt" | cut -d. -f1)
payload=$(echo "$jwt" | cut -d. -f2)
signature=$(echo "$jwt" | cut -d. -f3)

header_dec=$(echo "$header" | base64 -d 2>/dev/null)
payload_dec=$(echo "$payload" | base64 -d 2>/dev/null)

header_dec_jq=$(echo "$header_dec" | jq)
payload_dec_jq=$(echo "$payload_dec" | jq)

echo "HEADER:"
printf "%s\n%s\n%s", "$header", "$header_dec", "$header_dec_jq"
echo "PAYLOAD:"
printf "%s\n%s\n%s", "$payload", "$payload_dec", "$payload_dec_jq"
echo "SIGNATURE:"
echo "$signature"

echo "------"

echo "Encoding from -h -p"
header_enc=$(echo -n "$header_supp" | base64 | tr -d '=' | tr -d '\t\r\n')
payload_enc=$(echo -n "$payload_supp" | base64 | tr -d '=' | tr -d '\t\r\n')
printf "%s\n%s", "$header_enc", "$header_supp"
echo "---"
printf "%s\n%s", "$payload_enc", "$payload_supp"