This authentication method operates similarly to
    password except that it uses RADIUS
    as the password verification method. RADIUS is used only to validate
    the user name/password pairs. Therefore the user must already
    exist in the database before RADIUS can be used for
    authentication.
   
    When using RADIUS authentication, an Access Request message will be sent
    to the configured RADIUS server. This request will be of type
    Authenticate Only, and include parameters for
    user name, password (encrypted) and
    NAS Identifier. The request will be encrypted using
    a secret shared with the server. The RADIUS server will respond to
    this server with either Access Accept or
    Access Reject. There is no support for RADIUS accounting.
   
Multiple RADIUS servers can be specified, in which case they will be tried sequentially. If a negative response is received from a server, the authentication will fail. If no response is received, the next server in the list will be tried. To specify multiple servers, put the names within quotes and separate the server names with a comma. If multiple servers are specified, all other RADIUS options can also be given as a comma separate list, to apply individual values to each server. They can also be specified as a single value, in which case this value will apply to all servers.
The following configuration options are supported for RADIUS:
radiusserversThe name or IP addresses of the RADIUS servers to connect to. This parameter is required.
radiussecretsThe shared secrets used when talking securely to the RADIUS server. This must have exactly the same value on the PostgreSQL and RADIUS servers. It is recommended that this be a string of at least 16 characters. This parameter is required.
The encryption vector used will only be cryptographically strong if PostgreSQL is built with support for OpenSSL. In other cases, the transmission to the RADIUS server should only be considered obfuscated, not secured, and external security measures should be applied if necessary.
radiusports
         The port number on the RADIUS servers to connect to. If no port
         is specified, the default port 1812 will be used.
        
radiusidentifiers
         The string used as NAS Identifier in the RADIUS
         requests. This parameter can be used as a second parameter
         identifying for example which database user the user is attempting
         to authenticate as, which can be used for policy matching on
         the RADIUS server. If no identifier is specified, the default
         postgresql will be used.