JWT Signing Lambda

sign.js

const AWS = require("aws-sdk");
  const kms = new AWS.KMS();
  const util = require('util')

  const base64url = require("base64url");
  const keyId = '<YOUR_KEY_ID>'

  async function sign(headers, payload, key_arn) {

      payload.iat = Math.floor(Date.now() / 1000);

      const tomorrow = new Date()
      tomorrow.setDate(tomorrow.getDate() + 1)
      payload.exp = Math.floor(tomorrow.getTime() / 1000);

      let token_components = {
          header: base64url(JSON.stringify(headers)),
          payload: base64url(JSON.stringify(payload)),
      };

      let message = Buffer.from(token_components.header + "." + token_components.payload)

      let res = await kms.sign({
          Message: message,
          KeyId: keyId,
          SigningAlgorithm: 'RSASSA_PKCS1_V1_5_SHA_256',
          MessageType: 'RAW'
      }).promise()

      token_components.signature = res.Signature.toString("base64")
      .replace(/\+/g, '-')
      .replace(/\//g, '_')
      .replace(/=/g, '');

      return token_components.header + "." + token_components.payload + "." + token_components.signature;

  }

  let header = {
    "alg": "RS256",
    "typ": "JWT"
  }

  let payload = {
    "user_name": "yossale"
  }

  exports.handler = async (event) => {
      console.log("Start")
      let res = await sign(header, payload, keyId)
      console.log(`JWT token: [${res}]`)
  }