diff --git a/docs/topics/downloader-middleware.rst b/docs/topics/downloader-middleware.rst
index 1ca78ccc6..0ef3fb071 100644
--- a/docs/topics/downloader-middleware.rst
+++ b/docs/topics/downloader-middleware.rst
@@ -681,7 +681,9 @@ HttpProxyMiddleware
    * ``no_proxy``
 
    You can also set the meta key ``proxy`` per-request, to a value like
-   ``http://some_proxy_server:port``.
+   ``http://some_proxy_server:port`` or ``http://username:password@some_proxy_server:port``.
+   Keep in mind this value will take precedence over ``http_proxy``/``https_proxy``
+   environment variables, and it will also ignore ``no_proxy`` environment variable.
 
 .. _urllib: https://docs.python.org/2/library/urllib.html
 .. _urllib2: https://docs.python.org/2/library/urllib2.html
@@ -949,8 +951,16 @@ enable it for :ref:`broad crawls <topics-broad-crawls>`.
 HttpProxyMiddleware settings
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 
+.. setting:: HTTPPROXY_ENABLED
 .. setting:: HTTPPROXY_AUTH_ENCODING
 
+HTTPPROXY_ENABLED
+^^^^^^^^^^^^^^^^^
+
+Default: ``True``
+
+Whether or not to enable the :class:`HttpProxyMiddleware`.
+
 HTTPPROXY_AUTH_ENCODING
 ^^^^^^^^^^^^^^^^^^^^^^^
 
diff --git a/scrapy/downloadermiddlewares/httpproxy.py b/scrapy/downloadermiddlewares/httpproxy.py
index 98c87aa9c..0d5320bf8 100644
--- a/scrapy/downloadermiddlewares/httpproxy.py
+++ b/scrapy/downloadermiddlewares/httpproxy.py
@@ -20,23 +20,25 @@ class HttpProxyMiddleware(object):
         for type, url in getproxies().items():
             self.proxies[type] = self._get_proxy(url, type)
 
-        if not self.proxies:
-            raise NotConfigured
-
     @classmethod
     def from_crawler(cls, crawler):
+        if not crawler.settings.getbool('HTTPPROXY_ENABLED'):
+            raise NotConfigured
         auth_encoding = crawler.settings.get('HTTPPROXY_AUTH_ENCODING')
         return cls(auth_encoding)
 
+    def _basic_auth_header(self, username, password):
+        user_pass = to_bytes(
+            '%s:%s' % (unquote(username), unquote(password)),
+            encoding=self.auth_encoding)
+        return base64.b64encode(user_pass).strip()
+
     def _get_proxy(self, url, orig_type):
         proxy_type, user, password, hostport = _parse_proxy(url)
         proxy_url = urlunparse((proxy_type or orig_type, hostport, '', '', '', ''))
 
         if user:
-            user_pass = to_bytes(
-                '%s:%s' % (unquote(user), unquote(password)),
-                encoding=self.auth_encoding)
-            creds = base64.b64encode(user_pass).strip()
+            creds = self._basic_auth_header(user, password)
         else:
             creds = None
 
@@ -45,6 +47,15 @@ class HttpProxyMiddleware(object):
     def process_request(self, request, spider):
         # ignore if proxy is already set
         if 'proxy' in request.meta:
+            if request.meta['proxy'] is None:
+                return
+            # extract credentials if present
+            creds, proxy_url = self._get_proxy(request.meta['proxy'], '')
+            request.meta['proxy'] = proxy_url
+            if creds and not request.headers.get('Proxy-Authorization'):
+                request.headers['Proxy-Authorization'] = b'Basic ' + creds
+            return
+        elif not self.proxies:
             return
 
         parsed = urlparse_cached(request)
diff --git a/scrapy/settings/default_settings.py b/scrapy/settings/default_settings.py
index 24714a7a8..cb88bc2bf 100644
--- a/scrapy/settings/default_settings.py
+++ b/scrapy/settings/default_settings.py
@@ -174,6 +174,7 @@ HTTPCACHE_DBM_MODULE = 'anydbm' if six.PY2 else 'dbm'
 HTTPCACHE_POLICY = 'scrapy.extensions.httpcache.DummyPolicy'
 HTTPCACHE_GZIP = False
 
+HTTPPROXY_ENABLED = True
 HTTPPROXY_AUTH_ENCODING = 'latin-1'
 
 IMAGES_STORE_S3_ACL = 'private'

diff --git a/tests/test_downloadermiddleware_httpproxy.py b/tests/test_downloadermiddleware_httpproxy.py
index 2b26431a4..c77179ceb 100644
--- a/tests/test_downloadermiddleware_httpproxy.py
+++ b/tests/test_downloadermiddleware_httpproxy.py
@@ -1,11 +1,14 @@
 import os
 import sys
+from functools import partial
 from twisted.trial.unittest import TestCase, SkipTest
 
 from scrapy.downloadermiddlewares.httpproxy import HttpProxyMiddleware
 from scrapy.exceptions import NotConfigured
 from scrapy.http import Response, Request
 from scrapy.spiders import Spider
+from scrapy.crawler import Crawler
+from scrapy.settings import Settings
 
 spider = Spider('foo')
 
@@ -20,9 +23,10 @@ class TestDefaultHeadersMiddleware(TestCase):
     def tearDown(self):
         os.environ = self._oldenv
 
-    def test_no_proxies(self):
-        os.environ = {}
-        self.assertRaises(NotConfigured, HttpProxyMiddleware)
+    def test_not_enabled(self):
+        settings = Settings({'HTTPPROXY_ENABLED': False})
+        crawler = Crawler(spider, settings)
+        self.assertRaises(NotConfigured, partial(HttpProxyMiddleware.from_crawler, crawler))
 
     def test_no_enviroment_proxies(self):
         os.environ = {'dummy_proxy': 'reset_env_and_do_not_raise'}
@@ -47,6 +51,13 @@ class TestDefaultHeadersMiddleware(TestCase):
             self.assertEquals(req.url, url)
             self.assertEquals(req.meta.get('proxy'), proxy)
 
+    def test_proxy_precedence_meta(self):
+        os.environ['http_proxy'] = 'https://proxy.com'
+        mw = HttpProxyMiddleware()
+        req = Request('http://scrapytest.org', meta={'proxy': 'https://new.proxy:3128'})
+        assert mw.process_request(req, spider) is None
+        self.assertEquals(req.meta, {'proxy': 'https://new.proxy:3128'})
+
     def test_proxy_auth(self):
         os.environ['http_proxy'] = 'https://user:pass@proxy:3128'
         mw = HttpProxyMiddleware()
@@ -54,6 +65,11 @@ class TestDefaultHeadersMiddleware(TestCase):
         assert mw.process_request(req, spider) is None
         self.assertEquals(req.meta, {'proxy': 'https://proxy:3128'})
         self.assertEquals(req.headers.get('Proxy-Authorization'), b'Basic dXNlcjpwYXNz')
+        # proxy from request.meta
+        req = Request('http://scrapytest.org', meta={'proxy': 'https://username:password@proxy:3128'})
+        assert mw.process_request(req, spider) is None
+        self.assertEquals(req.meta, {'proxy': 'https://proxy:3128'})
+        self.assertEquals(req.headers.get('Proxy-Authorization'), b'Basic dXNlcm5hbWU6cGFzc3dvcmQ=')
 
     def test_proxy_auth_empty_passwd(self):
         os.environ['http_proxy'] = 'https://user:@proxy:3128'
@@ -62,6 +78,11 @@ class TestDefaultHeadersMiddleware(TestCase):
         assert mw.process_request(req, spider) is None
         self.assertEquals(req.meta, {'proxy': 'https://proxy:3128'})
         self.assertEquals(req.headers.get('Proxy-Authorization'), b'Basic dXNlcjo=')
+        # proxy from request.meta
+        req = Request('http://scrapytest.org', meta={'proxy': 'https://username:@proxy:3128'})
+        assert mw.process_request(req, spider) is None
+        self.assertEquals(req.meta, {'proxy': 'https://proxy:3128'})
+        self.assertEquals(req.headers.get('Proxy-Authorization'), b'Basic dXNlcm5hbWU6')
 
     def test_proxy_auth_encoding(self):
         # utf-8 encoding
@@ -72,6 +93,12 @@ class TestDefaultHeadersMiddleware(TestCase):
         self.assertEquals(req.meta, {'proxy': 'https://proxy:3128'})
         self.assertEquals(req.headers.get('Proxy-Authorization'), b'Basic bcOhbjpwYXNz')
 
+        # proxy from request.meta
+        req = Request('http://scrapytest.org', meta={'proxy': u'https://\u00FCser:pass@proxy:3128'})
+        assert mw.process_request(req, spider) is None
+        self.assertEquals(req.meta, {'proxy': 'https://proxy:3128'})
+        self.assertEquals(req.headers.get('Proxy-Authorization'), b'Basic w7xzZXI6cGFzcw==')
+
         # default latin-1 encoding
         mw = HttpProxyMiddleware(auth_encoding='latin-1')
         req = Request('http://scrapytest.org')
@@ -79,15 +106,21 @@ class TestDefaultHeadersMiddleware(TestCase):
         self.assertEquals(req.meta, {'proxy': 'https://proxy:3128'})
         self.assertEquals(req.headers.get('Proxy-Authorization'), b'Basic beFuOnBhc3M=')
 
+        # proxy from request.meta, latin-1 encoding
+        req = Request('http://scrapytest.org', meta={'proxy': u'https://\u00FCser:pass@proxy:3128'})
+        assert mw.process_request(req, spider) is None
+        self.assertEquals(req.meta, {'proxy': 'https://proxy:3128'})
+        self.assertEquals(req.headers.get('Proxy-Authorization'), b'Basic /HNlcjpwYXNz')
+
     def test_proxy_already_seted(self):
-        os.environ['http_proxy'] = http_proxy = 'https://proxy.for.http:3128'
+        os.environ['http_proxy'] = 'https://proxy.for.http:3128'
         mw = HttpProxyMiddleware()
         req = Request('http://noproxy.com', meta={'proxy': None})
         assert mw.process_request(req, spider) is None
         assert 'proxy' in req.meta and req.meta['proxy'] is None
 
     def test_no_proxy(self):
-        os.environ['http_proxy'] = http_proxy = 'https://proxy.for.http:3128'
+        os.environ['http_proxy'] = 'https://proxy.for.http:3128'
         mw = HttpProxyMiddleware()
 
         os.environ['no_proxy'] = '*'
@@ -104,3 +137,9 @@ class TestDefaultHeadersMiddleware(TestCase):
         req = Request('http://noproxy.com')
         assert mw.process_request(req, spider) is None
         assert 'proxy' not in req.meta
+
+        # proxy from meta['proxy'] takes precedence
+        os.environ['no_proxy'] = '*'
+        req = Request('http://noproxy.com', meta={'proxy': 'http://proxy.com'})
+        assert mw.process_request(req, spider) is None
+        self.assertEquals(req.meta, {'proxy': 'http://proxy.com'})

Scrapy ignores proxy credentials when using "proxy" meta key
Code `yield Request(link, meta={'proxy': 'http://user:password@ip:port’})` ignores user:password. 
Problem is solved by using header "Proxy-Authorization" with base64, but it is better to implement it inside Scrapy.
tests/test_downloadermiddleware_httpproxy.py::TestDefaultHeadersMiddleware::test_proxy_auth tests/test_downloadermiddleware_httpproxy.py::TestDefaultHeadersMiddleware::test_proxy_auth_empty_passwd tests/test_downloadermiddleware_httpproxy.py::TestDefaultHeadersMiddleware::test_proxy_auth_encoding
tests/test_downloadermiddleware_httpproxy.py::TestDefaultHeadersMiddleware::test_enviroment_proxies tests/test_downloadermiddleware_httpproxy.py::TestDefaultHeadersMiddleware::test_no_enviroment_proxies tests/test_downloadermiddleware_httpproxy.py::TestDefaultHeadersMiddleware::test_no_proxy tests/test_downloadermiddleware_httpproxy.py::TestDefaultHeadersMiddleware::test_not_enabled tests/test_downloadermiddleware_httpproxy.py::TestDefaultHeadersMiddleware::test_proxy_already_seted tests/test_downloadermiddleware_httpproxy.py::TestDefaultHeadersMiddleware::test_proxy_precedence_meta