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<chapter id="protocol">

<title>Frontend/Backend Protocol</title>

The server then sends an appropriate authentication request message,

to which the frontend must reply with an appropriate authentication

response message (such as a password).

For all authentication methods except GSSAPI, there is at most

For all authentication methods except GSSAPI and SSPI, there is at most

one request and one response. In some methods, no response

at all is needed from the frontend, and so no authentication request

occurs. For GSSAPI, multiple iterations of packets may be needed to

occurs. For GSSAPI and SSPI, multiple iterations of packets may be needed to

complete the authentication.

</para>

</listitem>

</varlistentry>

<varlistentry>

<term>AuthenticationSSPI</term>

<listitem>

<para>

The frontend must now initiate a SSPI negotiation. The frontend

will send a PasswordMessage with the first part of the SSPI

data stream in response to this. If further messages are needed,

the server will respond with AuthenticationGSSContinue.

</para>

</listitem>

</varlistentry>

<varlistentry>

<term>AuthenticationGSSContinue</term>

<listitem>

<para>

This message contains the response data from the previous step

of GSSAPI negotiation (AuthenticationGSS or a previous

AuthenticationGSSContinue). If the GSSAPI data in this message

of GSSAPI or SSPI negotiation (AuthenticationGSS, AuthenticationSSPI

or a previous AuthenticationGSSContinue). If the GSSAPI

or SSPI data in this message

indicates more data is needed to complete the authentication,

the frontend must send this data as another PasswordMessage. If

GSSAPI authentication is completed by this message, the server

</varlistentry>

<varlistentry>

<term>

AuthenticationSSPI (B)

</term>

<listitem>

<para>

<variablelist>

<varlistentry>

<term>

Byte1('R')

</term>

<listitem>

<para>

Identifies the message as an authentication request.

</para>

</listitem>

</varlistentry>

<varlistentry>

<term>

Int32(8)

</term>

<listitem>

<para>

Length of message contents in bytes, including self.

</para>

</listitem>

</varlistentry>

<varlistentry>

<term>

Int32(9)

</term>

<listitem>

<para>

Specifies that SSPI authentication is required.

</para>

</listitem>

</varlistentry>

</variablelist>

</para>

</listitem>

</varlistentry>

<varlistentry>

<term>

AuthenticationGSSContinue (B)

</term>

<listitem>

<para>

GSSAPI authentication data.

GSSAPIor SSPIauthentication data.

</para>

</listitem>

</varlistentry>