This middleware is added to the stack when `config.force_ssl = true`, and is passed the options set in `config.ssl_options`. It does three jobs to enforce secure HTTP requests:

1. TLS redirect: Permanently redirects http:// requests to https://
   with the same URL host, path, etc. Enabled by default. Set `config.ssl_options`
   to modify the destination URL
   (e.g. `redirect: { host: "", port: 8080 }`), or set
   `redirect: false` to disable this feature.

2. Secure cookies: Sets the `secure` flag on cookies to tell browsers they
   mustn't be sent along with http:// requests. Enabled by default. Set
   `config.ssl_options` with `secure_cookies: false` to disable this feature.

3. HTTP Strict Transport Security (HSTS): Tells the browser to remember
   this site as TLS-only and automatically redirect non-TLS requests.
   Enabled by default. Configure `config.ssl_options` with `hsts: false` to disable.

Set `config.ssl_options` with `hsts: { … }` to configure HSTS:

* `expires`: How long, in seconds, these settings will stick. Defaults to
  `180.days` (recommended). The minimum required to qualify for browser
  preload lists is `18.weeks`.
* `subdomains`: Set to `true` to tell the browser to apply these settings
  to all subdomains. This protects your cookies from interception by a
  vulnerable site on a subdomain. Defaults to `true`.
* `preload`: Advertise that this site may be included in browsers'
  preloaded HSTS lists. HSTS protects your site on every visit *except the
  first visit* since it hasn't seen your HSTS header yet. To close this
  gap, browser vendors include a baked-in list of HSTS-enabled sites.
  Go to to submit your site for inclusion.

To turn off HSTS, omitting the header is not enough. Browsers will remember the original HSTS directive until it expires. Instead, use the header to tell browsers to expire HSTS immediately. Setting `hsts: false` is a shortcut for `hsts: { expires: 0 }`.

Requests can opt-out of redirection with `exclude`:

config.ssl_options = { redirect: { exclude: -> request { request.path =~ /healthcheck/ } } }
HSTS_EXPIRES_IN = 15552000

Default to 180 days, the low end for and greater than the 18-week requirement for browser preload lists.

Class Public methods
# File actionpack/lib/action_dispatch/middleware/ssl.rb, line 46
def self.default_hsts_options
  { expires: HSTS_EXPIRES_IN, subdomains: false, preload: false }
new(app, redirect: {}, hsts: {}, secure_cookies: true, **options)
# File actionpack/lib/action_dispatch/middleware/ssl.rb, line 50
    def initialize(app, redirect: {}, hsts: {}, secure_cookies: true, **options)
      @app = app

      if options[:host] || options[:port]
        ActiveSupport::Deprecation.warn "          The `:host` and `:port` options are moving within `:redirect`:
          `config.ssl_options = { redirect: { host: …, port: … } }`.
        @redirect = options.slice(:host, :port)
        @redirect = redirect

      @exclude = @redirect && @redirect[:exclude] || proc { !@redirect }
      @secure_cookies = secure_cookies

      if hsts != true && hsts != false && hsts[:subdomains].nil?
        hsts[:subdomains] = false

        ActiveSupport::Deprecation.warn "          In Rails 5.1, The `:subdomains` option of HSTS config will be treated as true if
          unspecified. Set `config.ssl_options = { hsts: { subdomains: false } }` to opt out
          of this behavior.

      @hsts_header = build_hsts_header(normalize_hsts_options(hsts))
Instance Public methods
# File actionpack/lib/action_dispatch/middleware/ssl.rb, line 79
def call(env)
  request = env

  if request.ssl? do |status, headers, body|
      set_hsts_header! headers
      flag_cookies_as_secure! headers if @secure_cookies
    return redirect_to_https request unless