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+# Architecture
+The Swift API is HTTP-based. As described in the Swift documentation
+[1], clients first make a request to an authentication URL, providing
+a username and password. The reply contains a token which is used in
+all subsequent requests.
+Swift has a chain of filters through which all client requests go. The
+filters to use are configured with the pipeline parameter in
+ [pipeline:main]
+ pipeline = healthcheck cache tempauth proxy-server
+For the single sign authentication, we added a new filter called
+"kerbauth" and put it into the filter pipeline in place of tempauth.
+The filter checks the URL for each client request. If it matches the
+authentication URL, the client is redirected to a URL on a different
+server (on the same machine). The URL is handled by a CGI script, which
+is set up to authenticate the client with Kerberos negotiation, retrieve
+the user's system groups [2], store them in a memcache ring shared with
+the Swift server, and return the authentication token to the client.
+When the client provides the token as part of a resource request, the
+kerbauth filter checks it against its memcache, grants administrator
+rights based on the group membership retrieved from memcache, and
+either grants or denies the resource access.
+[2] The user data and system groups are usually provided by Red Hat
+ Enterprise Linux identity Management or Microsoft Active
+ Directory. The script relies on the system configuration to be set
+ accordingly (/etc/nsswitch.conf).
+The script began as a copy of the script from
+from tempauth middleware. It contains the following modifications, among
+In the __init__ method, we read the ext_authentication_url parameter
+from /etc/swift/proxy-server.conf. This is the URL that clients are
+redirected to when they access either the Swift authentication URL, or
+when they request a resource without a valid authentication token.
+The configuration in proxy-server.conf looks like this:
+ [filter:kerbauth]
+ use = egg:swiftkerbauth#kerbauth
+ ext_authentication_url =
+The authorize method was changed so that global administrator rights
+are granted if the user is a member of the auth_reseller_admin
+group. Administrator rights for a specific account like vol1 are
+granted if the user is a member of the auth_vol1 group. [3]
+The denied_response method was changed to return a HTTP redirect to
+the external authentication URL if no valid token was provided by the
+Most of the handle_get_token method was moved to the external
+authentication script. This method now returns a HTTP redirect.
+In the __call__ and get_groups method, we removed support for the
+HTTP_AUTHORIZATION header, which is only needed when Amazon S3 is
+Like, uses a Swift wrapper to access
+memcache. This wrapper converts the key to an MD5 hash and uses the
+hash value to determine on which of a pre-defined list of servers to
+store the data.
+[3] "auth" is the default reseller prefix, and would be different if
+ the reseller_prefix parameter in proxy-server.conf was set.
+## swift-auth CGI script
+swift-auth resides on an Apache server and assumes that Apache is
+configured to authenticate the user before this script is
+executed. The script retrieves the username from the REMOTE_USER
+environment variable, and checks if there already is a token for this
+user in the memcache ring. If not, it generates a new one, retrieves
+the user's system groups with "id -Gn USERNAME", stores this
+information in the memcache ring, and returns the token to the client.
+To allow the CGI script to connect to memcache, the SELinux booleans
+httpd_can_network_connect and httpd_can_network_memcache had to be
+The tempauth filter uses the uuid module to generate token
+strings. This module creates and runs temporary files, which leads to
+AVC denial messages in /var/log/audit/audit.log when used from an
+Apache CGI script. While the module still works, the audit log would
+grow quickly. Instead of writing an SELinux policy module to allow or
+to silently ignore these accesses, the swift-auth script uses the
+"random" module for generating token strings.
+Red Hat Enterprise Linux 6 comes with Python 2.6 which only provides
+method to list the locally defined user groups. To include groups from
+Red Hat Enterprise Linux Identity Management and in the future from
+Active Directory, the "id" command is run in a subprocess.