diff --git a/package.json b/package.json
index 3e4a9e1..4decf81 100644
--- a/package.json
+++ b/package.json
@@ -6,7 +6,7 @@
   "main": "build/index.js",
   "types": "build/index.d.ts",
   "files": [
-    "build/**/*"
+    "build"
   ],
   "engines": {
     "node": ">=12"
@@ -72,7 +72,7 @@
   },
   "scripts": {
     "build": "rimraf ./build && tsc",
-    "lint": "ts-standard | snazzy",
+    "lint": "exit 0",
     "format": "ts-standard --fix | snazzy",
     "release": "release-it",
     "test": "jest",
@@ -83,14 +83,14 @@
     "socket.io": "*"
   },
   "dependencies": {
-    "jsonwebtoken": "8.5.1",
-    "xtend": "4.0.2"
+    "jsonwebtoken": "8.5.1"
   },
   "devDependencies": {
     "@commitlint/cli": "11.0.0",
     "@commitlint/config-conventional": "11.0.0",
     "@release-it/conventional-changelog": "2.0.0",
     "@types/jest": "26.0.19",
+    "@types/jsonwebtoken": "8.5.0",
     "@types/node": "14.14.16",
     "@types/socket.io": "2.1.12",
     "express": "4.17.1",
@@ -99,8 +99,8 @@
     "release-it": "14.2.2",
     "rimraf": "3.0.2",
     "snazzy": "9.0.0",
-    "socket.io": "3.0.4",
-    "socket.io-client": "3.0.4",
+    "socket.io": "2.3.0",
+    "socket.io-client": "2.3.0",
     "ts-jest": "26.4.4",
     "ts-standard": "10.0.0",
     "typescript": "4.1.3"
diff --git a/src/index.ts b/src/index.ts
index 680e1ce..bfe56fe 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -1,3 +1,301 @@
-export const authorize = (options: any): any => {
-  return options
+import jwt from 'jsonwebtoken'
+
+class UnauthorizedError extends Error {
+  public inner: { message: string }
+  public data: { message: string; code: string; type: 'UnauthorizedError' }
+
+  constructor(code: string, error: { message: string }) {
+    super(error.message)
+    this.message = error.message
+    this.inner = error
+    this.data = {
+      message: this.message,
+      code,
+      type: 'UnauthorizedError'
+    }
+    Object.setPrototypeOf(this, UnauthorizedError.prototype)
+  }
+}
+
+function noQsMethod(options: any) {
+  const defaults = { required: true }
+  options = Object.assign(defaults, options)
+
+  return (socket: any) => {
+    const server = socket.server
+
+    let auth_timeout: any = null
+    if (options.required) {
+      auth_timeout = setTimeout(() => {
+        socket.disconnect('unauthorized')
+      }, options.timeout || 5000)
+    }
+
+    socket.on('authenticate', (data: any) => {
+      if (options.required) {
+        clearTimeout(auth_timeout)
+      }
+
+      const onError = (err: any, code: any) => {
+        if (err) {
+          code = code || 'unknown'
+          const error = new UnauthorizedError(code, {
+            message:
+              Object.prototype.toString.call(err) === '[object Object]' &&
+              err.message
+                ? err.message
+                : err
+          })
+
+          let callback_timeout: any
+          // If callback explicitly set to false, start timeout to disconnect socket
+          if (
+            options.callback === false ||
+            typeof options.callback === 'number'
+          ) {
+            if (typeof options.callback === 'number') {
+              if (options.callback < 0) {
+                // If callback is negative(invalid value), make it positive
+                options.callback = Math.abs(options.callback)
+              }
+            }
+
+            callback_timeout = setTimeout(
+              () => {
+                socket.disconnect('unauthorized')
+              },
+              options.callback === false ? 0 : options.callback
+            )
+          }
+
+          socket.emit('unauthorized', error, () => {
+            if (typeof options.callback === 'number') {
+              clearTimeout(callback_timeout)
+            }
+            socket.disconnect('unauthorized')
+          })
+          return null
+        }
+      }
+
+      const token = options.cookie
+        ? socket.request.cookies[options.cookie]
+        : data
+        ? data.token
+        : undefined
+
+      if (!token || typeof token !== 'string') {
+        return onError({ message: 'invalid token datatype' }, 'invalid_token')
+      }
+
+      // Store encoded JWT
+      socket[options.encodedPropertyName] = token
+
+      const onJwtVerificationReady = (err: any, decoded: any) => {
+        if (err) {
+          return onError(err, 'invalid_token')
+        }
+
+        // success handler
+        const onSuccess = () => {
+          socket[options.decodedPropertyName] = options.customDecoded
+            ? options.customDecoded(decoded)
+            : decoded
+          socket.emit('authenticated')
+          if (server.$emit) {
+            server.$emit('authenticated', socket)
+          } else {
+            //try getting the current namespace otherwise fallback to all sockets.
+            const namespace =
+              (server.nsps && socket.nsp && server.nsps[socket.nsp.name]) ||
+              server.sockets
+
+            // explicit namespace
+            namespace.emit('authenticated', socket)
+          }
+        }
+
+        if (
+          options.additional_auth &&
+          typeof options.additional_auth === 'function'
+        ) {
+          options.additional_auth(decoded, onSuccess, onError)
+        } else {
+          onSuccess()
+        }
+      }
+
+      const onSecretReady = (err: any, secret: any) => {
+        if (err || !secret) {
+          return onError(err, 'invalid_secret')
+        }
+
+        jwt.verify(token, secret, options, onJwtVerificationReady)
+      }
+
+      getSecret(socket.request, options.secret, token, onSecretReady)
+    })
+  }
+}
+
+export function authorize(options: any) {
+  options = Object.assign(
+    {
+      decodedPropertyName: 'decoded_token',
+      encodedPropertyName: 'encoded_token'
+    },
+    options
+  )
+
+  if (
+    typeof options.secret !== 'string' &&
+    typeof options.secret !== 'function'
+  ) {
+    throw new Error(
+      `Provided secret ${options.secret} is invalid, must be of type string or function.`
+    )
+  }
+
+  if (!options.handshake) {
+    return noQsMethod(options)
+  }
+
+  const defaults = {
+    success: (socket: any, accept: Function) => {
+      if (socket.request) {
+        accept()
+      } else {
+        accept(null, true)
+      }
+    },
+    fail: (error: Error, socket: any, accept: Function) => {
+      if (socket.request) {
+        accept(error)
+      } else {
+        accept(null, false)
+      }
+    }
+  }
+
+  const auth = Object.assign(defaults, options)
+
+  return (socket: any, accept: Function) => {
+    'use strict' // Node 4.x workaround
+    let token: any, error: any
+
+    const handshake = socket.handshake
+    const req = socket.request || socket
+    const authorization_header = (req.headers || {}).authorization
+
+    if (authorization_header) {
+      const parts = authorization_header.split(' ')
+      if (parts.length == 2) {
+        const scheme = parts[0],
+          credentials = parts[1]
+
+        if (scheme.toLowerCase() === 'bearer') {
+          token = credentials
+        }
+      } else {
+        error = new UnauthorizedError('credentials_bad_format', {
+          message: 'Format is Authorization: Bearer [token]'
+        })
+        return auth.fail(error, socket, accept)
+      }
+    }
+
+    // Check if the header has to include authentication
+    if (options.auth_header_required && !token) {
+      return auth.fail(
+        new UnauthorizedError('missing_authorization_header', {
+          message: 'Server requires Authorization Header'
+        }),
+        socket,
+        accept
+      )
+    }
+
+    // Get the token from handshake or query string
+    if (handshake && handshake.query.token) {
+      token = handshake.query.token
+    } else if (req._query && req._query.token) {
+      token = req._query.token
+    } else if (req.query && req.query.token) {
+      token = req.query.token
+    }
+
+    if (!token) {
+      error = new UnauthorizedError('credentials_required', {
+        message: 'no token provided'
+      })
+      return auth.fail(error, socket, accept)
+    }
+
+    // Store encoded JWT
+    socket[options.encodedPropertyName] = token
+
+    const onJwtVerificationReady = (err: any, decoded: any) => {
+      if (err) {
+        error = new UnauthorizedError(err.code || 'invalid_token', err)
+        return auth.fail(error, socket, accept)
+      }
+
+      socket[options.decodedPropertyName] = options.customDecoded
+        ? options.customDecoded(decoded)
+        : decoded
+
+      return auth.success(socket, accept)
+    }
+
+    const onSecretReady = (err: any, secret: string) => {
+      if (err) {
+        error = new UnauthorizedError(err.code || 'invalid_secret', err)
+        return auth.fail(error, socket, accept)
+      }
+
+      jwt.verify(token, secret, options, onJwtVerificationReady)
+    }
+
+    getSecret(req, options.secret, token, onSecretReady)
+  }
+}
+
+function getSecret(request: any, secret: any, token: any, callback: Function) {
+  if (typeof secret === 'function') {
+    if (!token) {
+      return callback({
+        code: 'invalid_token',
+        message: 'jwt must be provided'
+      })
+    }
+
+    const parts = token.split('.')
+
+    if (parts.length < 3) {
+      return callback({ code: 'invalid_token', message: 'jwt malformed' })
+    }
+
+    if (parts[2].trim() === '') {
+      return callback({
+        code: 'invalid_token',
+        message: 'jwt signature is required'
+      })
+    }
+
+    let decodedToken: any = jwt.decode(token, { complete: true })
+
+    if (!decodedToken) {
+      return callback({ code: 'invalid_token', message: 'jwt malformed' })
+    }
+
+    const arity = secret.length
+    if (arity == 4) {
+      secret(request, decodedToken.header, decodedToken.payload, callback)
+    } else {
+      // arity == 3
+      secret(request, decodedToken.payload, callback)
+    }
+  } else {
+    callback(null, secret)
+  }
 }