settings: Add an option to validate and add custom/self-signed certificates.

This PR helps to validate custom/self-signed certificates for servers
by saving the certificate file in certificates folder in user's appData folder.
We now use this certificate with the request while validating the server
when adding the organization. This validation of certificate is done by the request module itself.

Fixes: #126.

app/renderer/js/utils/certificate-util.js

@@ -0,0 +1,87 @@
+'use strict';
+
+const { app, dialog } = require('electron').remote;
+const fs = require('fs');
+const path = require('path');
+const JsonDB = require('node-json-db');
+const Logger = require('./logger-util');
+const { initSetUp } = require('./default-util');
+
+initSetUp();
+
+const logger = new Logger({
+	file: `certificate-util.log`,
+	timestamp: true
+});
+
+let instance = null;
+const certificatesDir = `${app.getPath('userData')}/certificates`;
+
+class CertificateUtil {
+	constructor() {
+		if (instance) {
+			return instance;
+		} else {
+			instance = this;
+		}
+
+		this.reloadDB();
+		return instance;
+	}
+	getCertificate(server, defaultValue = null) {
+		this.reloadDB();
+		const value = this.db.getData('/')[server];
+		if (value === undefined) {
+			return defaultValue;
+		} else {
+			return value;
+		}
+	}
+	// Function to copy the certificate to userData folder
+	copyCertificate(server, location, fileName) {
+		let copied = false;
+		const filePath = `${certificatesDir}/${fileName}`;
+		try {
+			fs.copyFileSync(location, filePath);
+			copied = true;
+		} catch (err) {
+			dialog.showErrorBox(
+				'Error saving certificate',
+				'We encountered error while saving the certificate.'
+			);
+			logger.error('Error while copying the certificate to certificates folder.');
+			logger.error(err);
+			console.log(err);
+		}
+		return copied;
+	}
+	setCertificate(server, fileName) {
+		const filePath = `${certificatesDir}/${fileName}`;
+		this.db.push(`/${server}`, filePath, true);
+		this.reloadDB();
+	}
+	removeCertificate(server) {
+		this.db.delete(`/${server}`);
+		this.reloadDB();
+	}
+	reloadDB() {
+		const settingsJsonPath = path.join(app.getPath('userData'), '/certificates.json');
+		try {
+			const file = fs.readFileSync(settingsJsonPath, 'utf8');
+			JSON.parse(file);
+		} catch (err) {
+			if (fs.existsSync(settingsJsonPath)) {
+				fs.unlinkSync(settingsJsonPath);
+				dialog.showErrorBox(
+					'Error saving settings',
+					'We encountered error while saving the certificate.'
+				);
+				logger.error('Error while JSON parsing certificates.json: ');
+				logger.error(err);
+			}
+		}
+		this.db = new JsonDB(settingsJsonPath, true, true);
+	}
+}
+
+module.exports = new CertificateUtil();