Sproxy2

HTTP proxy for authenticating users via OAuth2.

Motivation

This is overhaul of original Sproxy. See ChangeLog.md for the differences.

Why use a proxy for doing OAuth2? Isn't that up to the application?

• sproxy is secure by default. No requests make it to the web server if they haven't been explicitly whitelisted.
• sproxy is independent. Any web application written in any language can use it.

Use cases

• Existing web applications with concept of roles. For example, Mediawiki, Jenkins, Icinga Web 2. In this case you configure Sproxy to allow unrestricted access to the application for some groups defined by Sproxy. These groups are mapped to the application roles. There is a plugin for Jenkins which can be used for this. Mediawiki and Icinga Web 2 were also successfully deployed in this way, though it required changes to their source code.

• New web applications designed to work specifically behind Sproxy. In this case you define Sproxy rules to control access to the application's API. It would likely be a single-page application. Examples are MyWatch and Juan de la Cosa

How it works

When an HTTP client makes a request, Sproxy checks for a session cookie. If it doesn't exist (or it's invalid, expired), it responses with HTTP status 511 with the page, where the user can choose an OAuth2 provider to authenticate with. Finally, we store the the email address in a session cookie: signed with a hash to prevent tampering, set for HTTP only (to prevent malicious JavaScript from reading it), and set it for secure (since we don't want it traveling over plaintext HTTP connections).

From that point on, when sproxy detects a valid session cookie it extracts the email, checks it against the access rules, and relays the request to the back-end server (if allowed).

Permissions system

Permissions are stored in a PostgreSQL database. See sproxy.sql for details. Here are the main concepts:

• A group is identified by a name. Every group has
  • members (identified by email address, through group_member) and
  • associated privileges (through group_privilege).
• A privilege is identified by a name and a domain. It has associated rules (through privilege_rule) that define what the privilege gives access to.
• A rule is a combination of sql patterns for a domain, a path and an HTTP method. A rule matches an HTTP request, if all of these components match the respective attributes of the request. However of all the matching rules only the rule with the longest path pattern will be used to determine whether a user is allowed to perform a request. This is often a bit surprising, please see the following example:

Do note that Sproxy2 fetches only group_member, group_privilege and privilege_rule tables, because only these tables are used for authorization. The other tables serve for data integrity.

Keep in mind that:

• Domains are converted into lower case (coming from PostgreSQL or HTTP requests).
• Emails are converted into lower case (coming from PostgreSQL or OAuth2 providers).
• Groups are case-sensitive and treated as is.
• HTTP methods are case-sensitive.
• HTTP query parameters are ignored when matching a request against the rules.
• Privileges are case-sensitive and treated as is.
• SQL wildcards (_ and %) are supported for emails, domains, paths.

Privileges example

Consider this group_privilege and privilege_rule relations:

With this setup, everybody (that is readers, editors and administratorss) will have access to e.g. /imgs/logo.png and /favicon.ico, but only administrators will have access to /admin/index.php, because the longest matching path pattern is /admin/% and only administrators have the admin privilege.

Likewise readers have no access to e.g. /wiki/edit/delete_everything.php.

HTTP headers passed to the back-end server

All Sproxy headers are UTF8-encoded.

X-Groups denotes an intersection of the groups the visitor belongs to and the groups that granted access:

Logout

Hitting the endpoint /.sproxy/logout will invalidate the session cookie. The user will be redirected to / after logout.

Robots

Since all sproxied resources are private, it doesn't make sense for web crawlers to try to index them. In fact, crawlers will index only the login page. To prevent this, sproxy returns the following for /robots.txt:

User-agent: *
Disallow: /

Requirements

Sproxy2 is written in Haskell with GHC. All required Haskell libraries are listed in sproxy2.cabal. Use cabal-install to fetch and build all pre-requisites automatically.

Installation

$ git clone https://github.com/zalora/sproxy2.git
$ cd sproxy2
$ cabal install

Configuration

By default sproxy2 will read its configuration from sproxy.yml. There is example file with documentation sproxy.yml.example. You can specify a custom path with:

sproxy2 --config /path/to/sproxy.yml