This documentation is for Dovecot v2.x, see wiki1 for v1.x documentation.
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= Authentication policy support =

Dovecot supports (v2.2.25+) external authentication policy server. This server can be used to decide whether the connecting user is permitted, tarpitted or outright rejected. While dovecot can do tarpitting and refusal on it's own, this adds support for making cluster-wide decisions to make it easier to deter and defeat bruteforce attacks.

== Configuration ==

The auth-policy server is a core feature and does not require plugin(s) to work. To activate this feature, you need to configure it.


 * '''auth_policy_server_url''': URL of the policy server, url is appended with ?command=allow/report unless it ends with '&', at which just command=allow/report is added.
  * ''Default'': None ('''REQUIRED''' configuration)
 * '''auth_policy_server_api_header''': Header and value to add to request (for API authentication)
  * ''Default'': None (No authentication is done)
  * See https://en.wikipedia.org/wiki/Basic_access_authentication#Client_side
  * Example: {{{Authorization: Basic <base64-encoded value>}}}
 * '''auth_policy_server_timeout_msecs''': Request timeout in milliseconds
  * ''Default'': {{{auth_policy_server_timeout_msecs = 2000}}}
 * '''auth_policy_hash_mech''': Hash mechanism to use for password, you can use any hash mechanism supported by Dovecot (md4,md5,sha1,sha256,sha512)
  * ''Default'': {{{auth_policy_hash_mech = sha256}}}
 * '''auth_policy_hash_nonce''': Cluster-wide nonce to add to hash
  * ''Default'': None ('''REQUIRED''' configuration)
 * '''auth_policy_request_attributes''': Request attributes specification (see attributes section below)
  * ''Default'': {{{auth_policy_request_attributes = login=%{orig_username} pwhash=%{hashed_password} remote=%{real_rip}}}}
 * '''auth_policy_reject_on_fail''': If policy request fails for some reason should users be rejected
  * ''Default'': {{{auth_policy_reject_on_fail = no}}}
 * '''auth_policy_hash_truncate''': How many '''bits''' to use from password hash.
  * ''Default'': {{{auth_policy_hash_truncate = 12}}}

== Password hash algorithm ==

To generate the hash, you concatenate nonce, login name, nil byte, password and run it through the hash algorithm once. The hash is truncated when truncation is set to non-zero. The hash is truncated by first choosing bits from MSB to byte boundary (rounding up), then right-shifting the remainding bits.

{{{
hash = H(nonce||user||'\x00'||password)
bytes = round8(bits*8)
hash = HEX(hash[0:bytes] >> (bytes-bits*8))
}}}

== Request attributes ==

Auth policy server requests are JSON requests. The JSON format can be specified with auth_policy_request_attributes. The syntax is key=value pairs, and key can contain one or more / to designate that a JSON object should be made. For example:

{{{
login=%{orig_username} pwhash=%{hashed_password} remote=%{real_rip}
}}}

produces

{{{
{"login":"john.doe","pwhash":"1234","remote":"127.0.0.1"}
}}}

And

{{{
login=%{orig_username} pwhash=%{hashed_password} remote=%{real_rip} attrs/cos=%{userdb:cos}
}}}
produces
{{{
{"login":"john.doe","pwhash":"1234","remote":"127.0.0.1", "attrs":{"cos":"premium"}}
}}}

== Response ==

{{{
{"status":-1,"msg":"go away"}
}}}

{{{status}}} values: see below

== Mode of operation ==

=== Auth policy check: Authentication ''before'' userdb/passdb ===

First query is done '''before''' password and user databases are consulted. This means that any userdb/passdb attributes are left empty.

The command used here is 'allow' and will appear on the URL as command=allow.

{{{status}}} result values:
 * '''-1''': Reject
 * '''0''': Accept
 * '''(Any other positive value)''': Tarpit for this number of seconds.

=== Auth policy check: Authentication ''after'' successful userdb/passdb lookup ===

Second lookup is done '''after''' authentication succeeds.

The command used here is 'allow' and will appear on the URL as command=allow.

{{{status}}} result values:
 * '''-1''': Authentication fail
 * '''>= 0''': Authentication succeed

=== Auth policy check: Reporting after authentication succeeds ===

A report request is sent at end of authentication.

The command used here is 'report' and will appear on the URL as command=report.

The JSON request is sent with two additional attributes:
 * '''success''': boolean true/false depending on whether the overall authentication succeeded
 * '''wf_reject''': boolean true/false whether the failure was due to policy server

{{{status}}} result value is ignored.

== External Auth Policy Servers ==

 * http://oxpedia.org/wiki/index.php?title=AppSuite:Dovecot_Antiabuse_Shield
Moved to https://doc.dovecot.org/configuration_manual/authentication/auth_policy/

None: Authentication/Policy (last edited 2022-02-04 23:22:47 by TimoSirainen)