[HTTP] has a number of possible authentication schemes. In practice you are only likely to have to deal with Basic and [NTLM] (which is a Microsoft specific one).

**HTTP Basic Authentication**

[D. J. Hagberg] styles much the same as
======
proc geturl_auth {url username password} {
    set auth "Basic [base64::encode $username:$password]"
    set headerl [list Authorization $auth]
    set tok [http::geturl $url -headers $headerl]
    set res [http::data $tok]
    http::cleanup $tok
    return $res
}
======

Thanks to [Pat Thoyts] for this example of use of [http] authentication for proxies:
======
package require base64 ;# tcllib
package require http   ;# tcl

proc buildProxyHeaders {username password} {
    return [list "Proxy-Authorization" \
            [concat "Basic" [base64::encode $username:$password]]]
}

# Example...
proc fetch {url} {
    set tok [http::geturl $url -headers [buildProxyHeaders USERNAME PASSWORD]]
         
    # Process returned HTML ...
         
    http::cleanup $tok
}
======
Pat mentions that [TkChat] uses just such an approach.

Notice the distinct uses of "Authorization" and "Proxy-Authorization", about which [PT] writes:
    :   ''“Proxy-Authorization is used by HTTP [proxy] servers to decide if they are going to forward your request. This is typically used by corporate networks to provide accountability for web access. The Authorization header is used to authenticate you to the endpoint server. The Proxy-Authorization will never leave your local network - the Authorization header is passed all the way along to the final host.”''

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See also [autoproxy] for simple handling of proxy authentication. [[[PT]]]
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**NTLM Authentication**
[MC], June 7, 2006: Now that the [SASL] module in [tcllib] has support for [NTLM], does anyone have a simillar example using [NTLM]-authentication?

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D. Holmes, June 20, 2006:  Regarding the request for an NTLM example, I dug into this and found that it won't work with the http package.  NTLM requires keep-alive (or http 1.1) to work.  I wish http 1.1 (with ntlm and other authentication) into the core.  Anyway, I tried the SASL module for http athentication with NTLM and it failed.  I ended up using the ntlm code in tkabber with a hacked up chunk of code from http to receive http/1.1



----
**HTTP Digest Authentication**

This is a much better authentication method than Basic. However, it isn't much used yet.
The following package illustrates how to generate the Digest header on demand. At some point this will be made more useful to HTTP clients.

Currently to use this you would pass your http package token to the Parse method to have it return the options needed for the Response command. To generate the http header, you pass this result of to Header
In code terms:
======
set hdr {}
while {1} {
    set tok [http::geturl http:/www.authenticate/ -headers $hdr]
    if {[http::ncode $tok] == 401} {
        set args [digest::Parse $tok]
        set hdr [list Authorization [eval [list digest::Header] $args]]
        http::cleanup $tok
    } else {
        break
    }
}
======
----
======
# digest.tcl - Copyright (C) 2002 Pat Thoyts <pathoyts@users.sourceforge.net>
#
# Implement HTTP Digest Authentication
#
#
# The page handler needs to process headers. If we receive a
# 401 Unauthorised or the proxy equivalent we may get:
# WWW-Authenticate: Digest 
#       realm="testrealm@host.com",
#       qop="auth,auth-int",
#       nonce="dcd98b7102dd2f0e8b11d0f600bfb0c093",
#       opaque="5ccc069c403ebaf9f0171e9517f40e41"
#
# qop auth as below, auth-int includes a md5 sum of the page data too.
# No qop means a different final response calculation (without nonce values).
# 
# After a successful transaction you get an Authentication-Info header.
# The nextnonce value should be used to calculation the next Authentication
# header
# You may get a rspauth which can be used by the client to validate the
# server's response.
 
package require http 2.0;               # tcl core
package require md5; 2.0                # tcllib
 
namespace eval digest {
     variable version 1.0
     variable rcsid {
         $Id: 6087,v 1.13 2006-06-21 06:00:24 jcw Exp $
     }
 
     variable noncecount
     if {![info exists noncecount]} {
         array set noncecount {}
     }
 }
 
 proc digest::Header {args} {
     foreach {elt val} [eval Response $args] {
         lappend r "$elt=\"$val\""
     }
     return [concat Digest [join $r ", "]]
 }
 
 
 proc digest::Parse {token} {
     upvar $token state
     set r {}
 
     if {$state(querylength) < 1} {
         lappend r -cmd GET
     } else {
         lappend r -cmd POST
     }
     lappend r -uri $state(url)
 
     set ndx [lsearch -exact $state(meta) "WWW-Authenticate"]
     if {$ndx < 0} {
         return -code error "no WWW-Authenticate header found"
     }
     incr ndx
     set auth [lindex $state(meta) $ndx]
     if {![string match Digest* $auth]} {
         return -code error "this is not Digest auth"
     }
     foreach pair [split [string range $auth 7 end] ","] {
         regexp {([^=]+)=(.*)} [string trim $pair] -> name value
         lappend r -$name [string trim $value "\""]
     }
     return $r
 }
 
 proc digest::GetUserInfo {{user {}} {passwd {}}} {
     package require BWidget
     return [PasswdDlg .digestUserDetails \
                 -parent {} \
                 -transient 0 \
                 -logintext $user \
                 -passwdtext $passwd]
 }
 
 proc digest::Response {args} {
     variable noncecount
 
     array set opts [list user {} passwd {} qop {} \
                         getinfo [namespace origin GetUserInfo]]
     foreach {opt value} $args {
         switch -glob -- $opt {
             -get*  {
                 if {[info command $value] == {}} {
                     return -code error "invalid argument:\
                            \"$value\" is not a command"
                 }
                 set opts(getinfo) $value
             }
             -us*   { set opts(user) $value }
             -p*    { set opts(passwd) $value }
             -nonce { set opts(nonce) $value }
             -qop   { set opts(qop) $value }
             -realm { set opts(realm) $value }
             -cmd   { set opts(cmd) $value }
             -uri   { set opts(uri) $value }
             -op*   { set opts(opaque) $value }
             -cnon* { set opts(cnonce) $value }
             -algo* { set opts(alogrithm) $value }
             -domain { set opts(domain) $value}
             default {
                 return -code error "invalid option \"$opt\": must be one of\
                      -username, -password, -getinfo, -nonce, -qop, -realm,\
                      -cmd, -uri, -operation, -algorithm, -domain or -cnonce"
             }
         }
     }
 
     # Check we have everything we need.
     foreach elt [list nonce realm cmd uri] {
         if {![info exists opts($elt)]} {
             return -code error "invalid arguments: \"$elt\" must be supplied"
         }
     }
 
     # For testing - permit the client nonce value to be specified.
     if {![info exists opts(cnonce)]} {
         set opts(cnonce) [format %08x [clock clicks]]
     }
 
     # Only MD5 is acceptable as a calculation algorithm (sec: 3.2.1)
     if {[info exists opts(algorithm)]} {
         if {![string match "MD5*" $opts(algorithm)]} {
             return -code error "invalid algorithm spceified:\
                 \"$opts(algorithm)\" is not supported."
         }
     }
 
     # Calculate the nonce count value: - check server as well as realm?
     if {![info exists noncecount($opts(nonce))]} {
         set noncecount($opts(nonce)) 0
     }
     set nc [incr noncecount($opts(nonce))]
 
     # Prompt for password and user interactively if not supplied.
     if {$opts(user) == {} || $opts(passwd) == {}} {
         set r [$opts(getinfo) $opts(user) $opts(passwd)]
         foreach {opts(user) opts(passwd)} $r {}
     }
 
     # Build the response
     set A1 [string tolower [md5::md5 -hex "$opts(user):$opts(realm):$opts(passwd)"]]
     set A2 [string tolower [md5::md5 -hex "$opts(cmd):$opts(uri)"]]
     set nc [format %08u $nc]
 
     switch -exact -- $opts(qop) {
         {} {
             set response [string tolower [md5::md5 -hex "$A1:$opts(nonce):$A2"]]
         }
         auth {
             set response [string tolower [md5::md5 -hex "$A1:$opts(nonce):$nc:$opts(cnonce):$opts(qop):$A2"]]
         }
         default {
             return -code error ""
         }
     }
 
     set result [list \
                     username  $opts(user) \
                     realm     $opts(realm) \
                     nonce     $opts(nonce) \
                     uri       $opts(uri) \
                     qop       $opts(qop) \
                     nc        $nc \
                     cnonce    $opts(cnonce) \
                     response  $response]
     if {[info exists opts(opaque)]} {
         lappend result opaque $opts(opaque)
     }
     
     return $result
}
 
# -------------------------------------------------------------------------
 
package provide digest $::digest::version
 
# -------------------------------------------------------------------------
 
# Validation: see RFC2617 section 3.5
# We should be producing a header like:
# Digest username="Mufasa",
#   realm="testrealm@host.com",
#   nonce="dcd98b7102dd2f0e8b11d0f600bfb0c093",
#   uri="/dir/index.html",
#   qop="auth",
#   nc="00000001",
#   cnonce="0a4f113b",
#   response="6629fae49393a05397450978507c4ef1",
#   opaque="5ccc069c403ebaf9f0171e9517f40e41"
 
proc digest::Test {} {
     set r [digest::Response -user Mufasa \
                -pass "Circle Of Life" \
                -realm "testrealm@host.com" \
                -qop "auth" \
                -nonce "dcd98b7102dd2f0e8b11d0f600bfb0c093" \
                -opaque "5ccc069c403ebaf9f0171e9517f40e41" \
                -uri "/dir/index.html" \
                -cmd "GET" \
                -cnonce "0a4f113b"]
}
 
proc digest::Validate {} {
     variable noncecount
     array set valid {
         username "Mufasa"
         realm    "testrealm@host.com"
         nonce    "dcd98b7102dd2f0e8b11d0f600bfb0c093"
         uri      "/dir/index.html"
         qop      "auth"
         nc       "00000001"
         cnonce   "0a4f113b"
         response "6629fae49393a05397450978507c4ef1"
         opaque   "5ccc069c403ebaf9f0171e9517f40e41"
     }
 
     array set test [Test]
 
     # account for multiple runs of the test (nc is incremented)
     set valid(nc) [format %08u $noncecount($valid(nonce))]
 
     foreach key [array names valid] {
         if {[string compare $valid($key) $test($key)] != 0} {
             return -code error "validation error: for \"$key\"\
                    \"$test($key)\" should be \"$valid($key)\""
         }
     }
}
======

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See also: A lot of sites use [Cookies] to do authentication and [pop3 authentication].

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