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Example for decoding a JWT Payload with your Shell (bash, zsh...)

Setup

Add this to your .profile, .bashrc, .zshrc...

decode_base64_url() {
  local len=$((${#1} % 4))
  local result="$1"
  if [ $len -eq 2 ]; then result="$1"'=='
  elif [ $len -eq 3 ]; then result="$1"'=' 
  fi
  echo "$result" | tr '_-' '/+' | openssl enc -d -base64
}

decode_jwt(){
   decode_base64_url $(echo -n $2 | cut -d "." -f $1) | jq .
}

# Decode JWT header
alias jwth="decode_jwt 1"

# Decode JWT Payload
alias jwtp="decode_jwt 2"

Usage

jwtp eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJzdWIiOiIxMjM0NTY3ODkwIiwibmFtZSI6IkpvaG4gRG9lIiwiYWRtaW4iOnRydWV9.TJVA95OrM7E2cBab30RMHrHDcEfxjoYZgeFONFh7HgQ

Output

{
  "sub": "1234567890",
  "name": "John Doe",
  "admin": true
}
@mvitz

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commented Sep 9, 2016

Hi, thanks for sharing. At least for me (Mac OS X 10.11.6, Bash 4.3.46(1)-release) the argument for base64 has to be -D and not -d.

@chriswhite199

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commented Jul 12, 2018

To pretty print the expiration field, amend the jq . to:

# For local tz
jq 'if .exp then (.expStr = (.exp|gmtime|strftime("%Y-%m-%dT%H:%M:%S %Z"))) else . end'

# For UTC
jq 'if .exp then (.expStr = (.exp|todate)) else . end'

Output:

{
  "sub": "user",
  "exp": 1531376297,
  "expStr": "2018-07-12T06:18:17 PST"
}
@lounagen

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commented Jan 10, 2019

openssl enc -d -base64 doesn't work out of the box on mac (mocos mojave, LibreSSL 2.6.5 openssl version ) with base64 long lines without carriage-returns.

Handle it to be linux/mac compliant with a dummy test on the base64 command:
base64 -d on linux (or mac with linux base64 tool) and base64 -D on mac

Forked here https://gist.github.com/lounagen/bdcf3e59122e80bae6da114352d0280c

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