Generate the client_secret for this: https://developer.apple.com/documentation/sign_in_with_apple/generate_and_validate_tokens

Apple SSO Client_Secret.rb

require 'jwt'

key_file = 'key.txt' # This is the .p8 file you download from developer.apple.com. Just rename it to key.txt
team_id = ''
client_id = ''
key_id = '' # This is the KeyID of the .p8 file when you create it

ecdsa_key = OpenSSL::PKey::EC.new IO.read key_file
puts "Found Key"
puts IO.read key_file
puts "Encrypting"

headers = {
  'kid' => key_id
}

claims = {
	'iss' => team_id,
	'iat' => Time.now.to_i,
	'exp' => Time.now.to_i + 86400*180,
	'aud' => 'https://appleid.apple.com',
	'sub' => client_id,
}

token = JWT.encode claims, ecdsa_key, 'ES256', headers

puts token