Error Message: openssl_sign(): supplied key param cannot be coerced into a private key

I had the same issue and found the answer here on StackOverFlow : https://stackoverflow.com/questions/51327584/how-to-generate-key-pair-for-php-jwt

1) generate private key:

openssl genrsa -out private.pem 2048

2) extract public key from private key:

openssl rsa -in private.pem -outform PEM -pubout -out public.pem

3) and example php code:

<?php
require_once('vendor/autoload.php');

use \Firebase\JWT\JWT;

$privateKey = file_get_contents('./private.pem');

$publicKey = file_get_contents('./public.pem');

$payload = [
  'data' => ['field1' => 1, 'field2' => 'string data'],
  "iss" => "http://example.org",
  "aud" => "http://example.com",
  "iat" => 1531498466,
  "eat" => 1557000000
];

$token = JWT::encode($payload, $privateKey, 'RS256');
echo "Token:\n" . print_r($token, true) . "\n";

$decoded = JWT::decode($token, $publicKey, ['RS256']);
$decoded_array = (array) $decoded;

echo "Decoded:\n" . print_r($decoded_array, true) . "\n";

Bonus: HS256 example

Since HS256 is symmetric algorithm, it does not require private/public key pairs.

You may use Your own blablabla-like random secret string, without using generators and etc:

<?php
require_once('vendor/autoload.php');

use \Firebase\JWT\JWT;

$secret = 'blablabla-secret-string'; 
// or You can save that random text in .jwt-secret  file and use this way
// $secret = file_get_contents('./.jwt-secret');

$payload = [
  'data' => ['field1' => 1, 'field2' => 'string data'],
  "iss" => "http://example.org",
  "aud" => "http://example.com",
  "iat" => 1531498466,
  "eat" => 1557000000
];

$token = JWT::encode($payload, $secret, 'HS256');
echo "HS256 Token:\n" . print_r($token, true) . "\n";

$decoded = JWT::decode($token, $secret, ['HS256']);
$decoded_array = (array) $decoded;

echo "HS256 Token decoded:\n" . print_r($decoded_array, true) . "\n";

nowakowskir / php-jwt

Error Message: openssl_sign(): supplied key param cannot be coerced into a private key #7