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Created Oct 13, 2009
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Memcached SASL Specification
Author: Dustin Sallings <>
Date: 2009-10-13 Wed
Table of Contents
1 Overview
2 Authentication Concepts
3 Protocol Definitions
3.1 Error Codes and Conditions
3.2 Authentication Requests
4 Error Reference
5 Command Reference
6 See Also
1 Overview
Most deployments of memcached today exist within trusted networks
where clients may freely connect to any server and the servers don't
discriminate against them.
There are cases, however, where memcached is deployed in untrusted
networks or where administrators would like to exercise a bit more
control over the clients that are connecting.
2 Authentication Concepts
Authentication is abstracted from the server using the Simple
Authentication and Security Layer.
Among other things, this provides administrators with consistent
credential management that is mostly independent from the services
that are authenticating clients.
3 Protocol Definitions
3.1 Error Codes and Conditions
There are two status codes provided by the SASL protocol to enable
3.1.1 Unauthorized
If a message is returned with a status code of 0x20, this is
considered an authentication or authorization failure.
This may be in response to an explicit authentication command
indicating the credentials were not accepted or the authorization was
otherwise not granted to access the server.
3.1.2 Continue Authentication
Some SASL mechanisms require multiple messages to be sent between the
client and server. If a server responds to an authentication message
with a status code of 0x21, this will indicate your client needs to do
more work to complete the authentication negotiation.
3.1.3 Authentication Not Supported
If a server responds to an authentication request indicating the
command is unknown (status 0x81), it likely doesn't support
authentication. It is generally acceptable for the client to consider
authentication successful when communicating to a server that doesn't
support authentication.
3.2 Authentication Requests
3.2.1 List Mechanisms
In order to negotiate authentication, a client may need to ask the
server what authentication mechanisms it supports.
A command 0x20 with no extras, key, or value will request a mechanism
list from the server. The mechanisms are returned as a
space-separated value.
3.2.2 Authentication Request
To begin an authentication request, send a request with command 0x21,
the requested mechanism as the key, and the initial authentication
data as the value if any is required for the chosen mechanism.
3.2.3 Authentication Continuation
If the authentication request responded with a continuation request
(status 0x21), the body will contain the data needed for computing the
next value in the authentication negotiation.
The next step's data will be transmitted similarly to the initial
step, but using command 0x22. Note that this includes the mechanism
within the key as in the initial request.
4 Error Reference
Status Code Meaning
0x20 Authentication required / Not Successful
0x21 Further authentication steps required.
5 Command Reference
Command OpCode Key Value
List Mechanisms 0x20 None None
Start Authentication 0x21 Mechanism Auth Data
Authentication Step 0x22 Mechanism Auth Data
6 See Also
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