diff --git a/.nvmrc b/.nvmrc
index 62f9457..25bf17f 100644
--- a/.nvmrc
+++ b/.nvmrc
@@ -1 +1 @@
-6
\ No newline at end of file
+18
\ No newline at end of file
diff --git a/config/config.json b/config/config.json
index 7109e2e..3025d6a 100644
--- a/config/config.json
+++ b/config/config.json
@@ -2,6 +2,8 @@
   "softwareStatementId": "",
   "clientScopes": "",
   "keyId": "",
+  "signingCert_passphrase": null,
+  "transportCert_passphrase": null,
   "tokenUrl": "https://matls-sso.openbankingtest.org.uk/as/token.oauth2",
   "tppTestUrl": "https://matls-api.openbankingtest.org.uk/scim/v2/participants/",
   "aud": "https://matls-sso.openbankingtest.org.uk/as/token.oauth2"
diff --git a/index.js b/index.js
index c2466f3..799ae42 100644
--- a/index.js
+++ b/index.js
@@ -1,17 +1,20 @@
-const
-fs = require('fs'),
-nJwt = require('njwt'),
-qs = require('qs'),
-request = require('axios'),
-https = require('https'),
-chalk = require('chalk'),
-boxen = require('boxen');
-
-console.log(chalk.bold.green(boxen("Open Banking Directory Access Token Acquisition Tool", {
-  margin: 1,
-  padding: 1,
-  style: 'double'
-})));
+const fs = require('fs'),
+  nJwt = require('njwt'),
+  qs = require('qs'),
+  request = require('axios'),
+  https = require('https'),
+  chalk = require('chalk'),
+  boxen = require('boxen');
+
+console.log(
+  chalk.bold.green(
+    boxen('Open Banking Directory Access Token Acquisition Tool', {
+      margin: 1,
+      padding: 1,
+      style: 'double',
+    })
+  )
+);
 console.log();
 
 // Load Private Key and config from files
@@ -19,41 +22,55 @@ const config = JSON.parse(fs.readFileSync(`${__dirname}/config/config.json`));
 const signingCert = fs.readFileSync(`${__dirname}/config/certSigning.pem`);
 const signingKey = fs.readFileSync(`${__dirname}/config/privateKeySigning.key`); // ES512
 const transportCert = fs.readFileSync(`${__dirname}/config/certTransport.pem`);
-const transportKey = fs.readFileSync(`${__dirname}/config/privateKeyTransport.key`); // ES512
+const transportKey = fs.readFileSync(
+  `${__dirname}/config/privateKeyTransport.key`
+); // ES512
 
 // Node doesn't support concatenated CAs in a single PEM
 // Read both files into the globalAgents file one at a time.
 const trustedCa = [
   `${__dirname}/config/root.pem`,
   `${__dirname}/config/issuingca.pem`,
-  `${__dirname}/config/signingca.pem`
+  `${__dirname}/config/signingca.pem`,
 ];
 
 const claims = {
-iss: config.softwareStatementId,
-sub: config.softwareStatementId,
-scope: config.clientScopes,
-aud: config.aud
+  iss: config.softwareStatementId,
+  sub: config.softwareStatementId,
+  scope: config.clientScopes,
+  aud: config.aud,
 };
-
-const created_jwt = nJwt.create(claims, signingKey, 'RS256');
+const created_jwt = nJwt.create(
+  claims,
+  {
+    key: signingKey,
+    passphrase:
+      config.signingCert_passphrase === null
+        ? undefined
+        : config.signingCert_passphrase,
+  },
+  'RS256'
+);
 created_jwt.setHeader('kid', config.keyId);
 const compacted_jwt = created_jwt.compact();
 
-console.log(chalk.bold.blue("Created JWT:"), compacted_jwt);
+console.log(chalk.bold.blue('Created JWT:'), compacted_jwt);
 console.log();
 
-
 //Blank the CA list and load only the MA ones
 var httpsAgent = https.globalAgent;
 https.globalAgent.options.ca = [];
 for (const ca of trustedCa) {
   https.globalAgent.options.ca.push(fs.readFileSync(ca));
   httpsAgent = new https.Agent({
-      cert: transportCert,
-      key: transportKey,
-      ca: https.globalAgent.options.ca,
-      rejectUnauthorized: true
+    cert: transportCert,
+    key: transportKey,
+    passphrase:
+      config.transportCert_passphrase === null
+        ? undefined
+        : config.transportCert_passphrase,
+    ca: https.globalAgent.options.ca,
+    rejectUnauthorized: true,
   });
 }
 
@@ -63,53 +80,55 @@ const tokenRequestSpec = {
   httpsAgent: httpsAgent,
   method: 'POST',
   data: qs.stringify({
-    'client_assertion_type': 'urn:ietf:params:oauth:client-assertion-type:jwt-bearer',
-    'grant_type': 'client_credentials',
-    'client_id': config.softwareStatementId,
-    'client_assertion': compacted_jwt,
-    'scope': config.clientScopes
-  })
+    client_assertion_type:
+      'urn:ietf:params:oauth:client-assertion-type:jwt-bearer',
+    grant_type: 'client_credentials',
+    client_id: config.softwareStatementId,
+    client_assertion: compacted_jwt,
+    scope: config.clientScopes,
+  }),
 };
 
-console.log(chalk.bold.blue("Requesting Access Token..."));
+console.log(chalk.bold.blue('Requesting Access Token...'));
 console.log();
 
-const errorHandler = function(error) {
+const errorHandler = function (error) {
   console.log(chalk.red.bold(error));
-  console.log(chalk.blue.bold("Response body:"));
-  console.log(error.response.data);
-  console.log(error.response.status);
+  console.log(chalk.blue.bold('Response body:'));
+  console.log(error.response?.data);
+  console.log(error.response?.status);
 };
 
 // Send request to get the token
 request(tokenRequestSpec)
-.then((response) => {
-  console.log(chalk.bold.blue("Token acquired:"), response.data.access_token);
-  console.log();
-
-  // Configure the request for test endpoint - list of Participants
-  const tppRequestSpec = {
-    url: config.tppTestUrl,
-    httpsAgent: httpsAgent, 
-    method: "GET",
-    headers: {
-      "Authorization": `Bearer ${response.data.access_token}`
-    }
-  };
-
-  return request(tppRequestSpec);
-
-})
-.then((response) => {
-
-  // Test request to get the list of Participants
-  response.data.Resources.forEach((participant) => {
-    const org = participant['urn:openbanking:organisation:1.0'];
-    const auth = participant['urn:trustframework:competentauthorityclaims:1.1'];
-    const authorisation =participant['urn:trustframework:competentauthorityclaims:1.1.Authorisations'];
-
-    console.log("-", org.OrganisationCommonName, "-", auth.Authorisations);
-  });
-
-})
-.catch(errorHandler);
\ No newline at end of file
+  .then((response) => {
+    console.log(chalk.bold.blue('Token acquired:'), response.data.access_token);
+    console.log();
+
+    // Configure the request for test endpoint - list of Participants
+    const tppRequestSpec = {
+      url: config.tppTestUrl,
+      httpsAgent: httpsAgent,
+      method: 'GET',
+      headers: {
+        Authorization: `Bearer ${response.data.access_token}`,
+      },
+    };
+
+    return request(tppRequestSpec);
+  })
+  .then((response) => {
+    // Test request to get the list of Participants
+    response.data.Resources.forEach((participant) => {
+      const org = participant['urn:openbanking:organisation:1.0'];
+      const auth =
+        participant['urn:trustframework:competentauthorityclaims:1.1'];
+      const authorisation =
+        participant[
+          'urn:trustframework:competentauthorityclaims:1.1.Authorisations'
+        ];
+
+      console.log('-', org.OrganisationCommonName, '-', auth.Authorisations);
+    });
+  })
+  .catch(errorHandler);