AnyEvent/MCP/Config.pm

=head1 NAME

AnyEvent::MCP::Config - named servers and derived MCP credentials

=head1 SYNOPSIS

   my $config = AnyEvent::MCP::Config->global;
   my $password = $config->credential ("basic", "agni", "alice");
   my $url = $config->url ("agni");

=head1 DESCRIPTION

An MCP server and its clients often need matching credentials. Rather than
maintaining a separate password for each server and user, this module can
derive them from one private master secret. A server name, optional username
and credential purpose each contribute to the result. A password derived for
one server is therefore not the password for another.

The shared file format is described in L<AnyEvent::MCP/GLOBAL CONFIGURATION>.
Loading this module does not read any files. The first call to C<global>
reads the configuration, ensures a master secret exists and caches the object
for the process.

A missing secret is generated using C<AnyEvent::MCP::random_bytes> and saved
when possible. Saving failure produces a warning; the generated secret remains
usable in this process, but another process might derive different credentials.
A supplied invalid secret is an error. Changing or losing the master secret
invalidates all credentials derived from it.

Derivation uses HKDF-SHA512 expansion with the random master key as its PRK.
Server name, username and credential purpose are separately length-prefixed,
so credentials for different servers, users or authentication methods differ.
Deriving a password does not create an account or configure the server to
accept it: authentication still belongs to the server.

=head1 METHODS

=head2 $config = AnyEvent::MCP::Config->global (file => $file)

Returns the cached global configuration. The first call accepts the same
arguments as C<new>; later calls return the same object without rereading
the file. Call this explicitly during program startup.

=head2 $config = AnyEvent::MCP::Config->new (file => $file)

Reads C<$file>, or the default file when omitted, and ensures a master
secret exists. Unlike C<global>, each call creates an independent object.
A missing file is allowed; other read errors are fatal. Sections are available
as C<< $config->{section}{$section} >>, each a hash reference of string
values. Named servers use C<[server NAME]>.

=head2 $config = AnyEvent::MCP::Config->init (file => $file)

Explicitly creates the configuration file with a random secret, mode 0600.
Creates missing parent directories with mode 0700. Fails if the file already
exists, so it cannot accidentally replace an existing secret.

=head2 $credential = $config->credential ($purpose, $name, $username)

Derives a 32-byte credential, returned as unpadded URL-safe Base64.
C<$purpose> is C<basic>, C<bearer> or C<cookie>. C<$name> is the server
name. C<$username> can be omitted for a server-wide credential.

This method does not require a corresponding server section.

=head2 $url = $config->url ($name, $username)

Returns the configured C<url> for C<$name>, replacing C<{cookie}> with the
derived cookie credential. C<$username> can be omitted.

The template supplies scheme, host, port, path and cookie placement explicitly.
This method neither contacts a server nor infers an ephemeral listening port.
The HTTP server does not consume this configuration automatically.

=cut

package AnyEvent::MCP::Config;

use common::sense;
use AnyEvent::MCP ();
use MIME::Base64 ();
use File::Basename ();
use File::Path ();
use Fcntl qw(O_WRONLY O_RDWR O_CREAT O_EXCL LOCK_EX);
use Errno qw(ENOENT);

our @ISA = qw(AnyEvent::MCP::Base);

sub _file {
   my $dir = $ENV{XDG_CONFIG_HOME}
      || ($ENV{HOME} || die "HOME is not set\n") . "/.config";

   "$dir/anyevent-mcp/global.ini"
}

my $global;

sub global {
   my $class = shift;

   $global ||= $class->new (@_)
}

sub new {
   my ($class, %kv) = @_;
   my $self = $class->SUPER::new (section => {}, %kv);
   $self->{file} = _file unless exists $self->{file};

   if (open my $fh, "<:encoding(UTF-8)", $self->{file}) {
      $self->_read ($fh);
      close $fh or die "$self->{file}: $!\n";
   } else {
      die "$self->{file}: $!\n" unless $! == ENOENT;
   }

   $self->_ensure_secret;

   die "$self->{file}: invalid secret; supply 128 hexadecimal digits\n"
      unless $self->{section}{global}{secret} =~ /\A[0-9a-fA-F]{128}\z/;

   $self
}

sub _read {
   my ($self, $fh) = @_;

   my @stat = stat $fh;
   die "$self->{file}: configuration must be private and owned by this user\n"
      if $stat[4] != $< || $stat[2] & 077;

   my $section = $self->{section}{global} ||= {};

   while (<$fh>) {
      next if /\A\s*(?:[#;]|\z)/;

      if (/\A\s*\[([^\]\r\n]+)\]\s*\z/) {
         $section = $self->{section}{$1} ||= {};
      } elsif (/\A\s*([^=\s]+)\s*=\s*(.*?)\s*\z/) {
         $section->{$1} = $2;
      } else {
         die "$self->{file}:$.: invalid configuration line\n";
      }
   }

}

sub _ensure_secret {
   my ($self) = @_;

   return if exists $self->{section}{global}{secret};

   my $secret = eval { unpack "H*", AnyEvent::MCP::random_bytes 64 };
   die "$@Supply a securely generated 128-digit hexadecimal secret in $self->{file}\n"
      if $@;

   eval {
      File::Path::mkpath (File::Basename::dirname ($self->{file}), 0, 0700);
      sysopen my $fh, $self->{file}, O_RDWR | O_CREAT, 0600
         or die "$self->{file}: $!\n";
      flock $fh, LOCK_EX or die "$self->{file}: $!\n";
      binmode $fh, ":encoding(UTF-8)";

      my $disk = bless { file => $self->{file}, section => {} }, ref $self;
      $disk->_read ($fh);

      unless (exists $disk->{section}{global}{secret}) {
         seek $fh, 0, 2 or die "$self->{file}: $!\n";
         print {$fh} "\n[global]\nsecret = $secret\n"
            or die "$self->{file}: $!\n";
         $disk->{section}{global}{secret} = $secret;
      }

      close $fh or die "$self->{file}: $!\n";
      $self->{section} = $disk->{section};
      1
   } or warn "Cannot save MCP master secret; credentials may only be stable for this process: $@";

   $self->{section}{global}{secret} = $secret
      unless exists $self->{section}{global}{secret};
}

sub init {
   my ($class, %kv) = @_;
   my $file = exists $kv{file} ? $kv{file} : _file;

   my $secret = AnyEvent::MCP::random_bytes 64;

   File::Path::mkpath (File::Basename::dirname ($file), 0, 0700);

   sysopen my $fh, $file, O_WRONLY | O_CREAT | O_EXCL, 0600
      or die "$file: $!\n";

   print {$fh} "[global]\nsecret = ", unpack ("H*", $secret), "\n"
      or die "$file: $!\n";
   close $fh or die "$file: $!\n";

   $class->new (file => $file)
}

sub credential {
   my ($self, $purpose, $name, $username) = @_;

   $username = "" unless defined $username;

   die "Unknown credential purpose '$purpose'\n"
      unless $purpose =~ /\A(?:basic|bearer|cookie)\z/;

   my $secret = $self->{section}{global}{secret};
   die "$self->{file}: missing or invalid secret\n"
      unless $secret =~ /\A[0-9a-fA-F]{128}\z/;

   my $info = pack "N/a*N/a*N/a*N/a*",
      "AnyEvent::MCP credential v1", $purpose,
      AnyEvent::MCP::utf8enc ($name), AnyEvent::MCP::utf8enc ($username);

   my $credential = MIME::Base64::encode_base64 (
      AnyEvent::MCP::hkdf_sha512_expand (pack ("H*", $secret), $info, 32), ""
   );
   $credential =~ y!+/=!-_!d;

   $credential
}

sub url {
   my ($self, $name, $username) = @_;

   my $url = $self->{section}{"server $name"}{url}
      or die "No URL configured for server '$name'\n";

   $url =~ s/\{cookie\}/$self->credential ("cookie", $name, $username)/ge;

   $url
}

1
Revision:	1.3
Committed:	Fri Oct 9 09:36:48 2026 UTC (4 weeks, 4 days ago) by root
Branch:	MAIN
Changes since 1.2:	+15 -7 lines
Log Message:	* empty log message *
#	User	Rev	Content
1	root	1.1	=head1 NAME
2
3			AnyEvent::MCP::Config - named servers and derived MCP credentials
4
5			=head1 SYNOPSIS
6
7			my $config = AnyEvent::MCP::Config->global;
8			my $password = $config->credential ("basic", "agni", "alice");
9			my $url = $config->url ("agni");
10
11			=head1 DESCRIPTION
12
13	root	1.3	An MCP server and its clients often need matching credentials. Rather than
14			maintaining a separate password for each server and user, this module can
15			derive them from one private master secret. A server name, optional username
16			and credential purpose each contribute to the result. A password derived for
17			one server is therefore not the password for another.
18
19			The shared file format is described in L<AnyEvent::MCP/GLOBAL CONFIGURATION>.
20			Loading this module does not read any files. The first call to C<global>
21			reads the configuration, ensures a master secret exists and caches the object
22			for the process.
23	root	1.1
24			A missing secret is generated using C<AnyEvent::MCP::random_bytes> and saved
25			when possible. Saving failure produces a warning; the generated secret remains
26	root	1.3	usable in this process, but another process might derive different credentials.
27			A supplied invalid secret is an error. Changing or losing the master secret
28			invalidates all credentials derived from it.
29	root	1.1
30			Derivation uses HKDF-SHA512 expansion with the random master key as its PRK.
31			Server name, username and credential purpose are separately length-prefixed,
32			so credentials for different servers, users or authentication methods differ.
33	root	1.3	Deriving a password does not create an account or configure the server to
34			accept it: authentication still belongs to the server.
35	root	1.1
36			=head1 METHODS
37
38			=head2 $config = AnyEvent::MCP::Config->global (file => $file)
39
40			Returns the cached global configuration. The first call accepts the same
41			arguments as C<new>; later calls return the same object without rereading
42			the file. Call this explicitly during program startup.
43
44			=head2 $config = AnyEvent::MCP::Config->new (file => $file)
45
46			Reads C<$file>, or the default file when omitted, and ensures a master
47			secret exists. Unlike C<global>, each call creates an independent object.
48			A missing file is allowed; other read errors are fatal. Sections are available
49			as C<< $config->{section}{$section} >>, each a hash reference of string
50			values. Named servers use C<[server NAME]>.
51
52			=head2 $config = AnyEvent::MCP::Config->init (file => $file)
53
54			Explicitly creates the configuration file with a random secret, mode 0600.
55			Creates missing parent directories with mode 0700. Fails if the file already
56			exists, so it cannot accidentally replace an existing secret.
57
58			=head2 $credential = $config->credential ($purpose, $name, $username)
59
60			Derives a 32-byte credential, returned as unpadded URL-safe Base64.
61			C<$purpose> is C<basic>, C<bearer> or C<cookie>. C<$name> is the server
62			name. C<$username> can be omitted for a server-wide credential.
63
64			This method does not require a corresponding server section.
65
66			=head2 $url = $config->url ($name, $username)
67
68			Returns the configured C<url> for C<$name>, replacing C<{cookie}> with the
69			derived cookie credential. C<$username> can be omitted.
70
71			The template supplies scheme, host, port, path and cookie placement explicitly.
72			This method neither contacts a server nor infers an ephemeral listening port.
73			The HTTP server does not consume this configuration automatically.
74
75			=cut
76
77			package AnyEvent::MCP::Config;
78
79			use common::sense;
80			use AnyEvent::MCP ();
81			use MIME::Base64 ();
82			use File::Basename ();
83			use File::Path ();
84			use Fcntl qw(O_WRONLY O_RDWR O_CREAT O_EXCL LOCK_EX);
85			use Errno qw(ENOENT);
86
87			our @ISA = qw(AnyEvent::MCP::Base);
88
89			sub _file {
90			my $dir = $ENV{XDG_CONFIG_HOME}
91			\|\| ($ENV{HOME} \|\| die "HOME is not set\n") . "/.config";
92
93			"$dir/anyevent-mcp/global.ini"
94			}
95
96			my $global;
97
98			sub global {
99			my $class = shift;
100
101			$global \|\|= $class->new (@_)
102			}
103
104			sub new {
105			my ($class, %kv) = @_;
106			my $self = $class->SUPER::new (section => {}, %kv);
107			$self->{file} = _file unless exists $self->{file};
108
109			if (open my $fh, "<:encoding(UTF-8)", $self->{file}) {
110			$self->_read ($fh);
111			close $fh or die "$self->{file}: $!\n";
112			} else {
113			die "$self->{file}: $!\n" unless $! == ENOENT;
114			}
115
116			$self->_ensure_secret;
117
118			die "$self->{file}: invalid secret; supply 128 hexadecimal digits\n"
119			unless $self->{section}{global}{secret} =~ /\A[0-9a-fA-F]{128}\z/;
120
121			$self
122			}
123
124			sub _read {
125			my ($self, $fh) = @_;
126
127			my @stat = stat $fh;
128			die "$self->{file}: configuration must be private and owned by this user\n"
129			if $stat[4] != $< \|\| $stat[2] & 077;
130
131			my $section = $self->{section}{global} \|\|= {};
132
133			while (<$fh>) {
134			next if /\A\s*(?:[#;]\|\z)/;
135
136			if (/\A\s\[([^\]\r\n]+)\]\s\z/) {
137			$section = $self->{section}{$1} \|\|= {};
138			} elsif (/\A\s([^=\s]+)\s=\s(.?)\s*\z/) {
139			$section->{$1} = $2;
140			} else {
141			die "$self->{file}:$.: invalid configuration line\n";
142			}
143			}
144
145			}
146
147			sub _ensure_secret {
148			my ($self) = @_;
149
150			return if exists $self->{section}{global}{secret};
151
152			my $secret = eval { unpack "H*", AnyEvent::MCP::random_bytes 64 };
153			die "$@Supply a securely generated 128-digit hexadecimal secret in $self->{file}\n"
154			if $@;
155
156			eval {
157			File::Path::mkpath (File::Basename::dirname ($self->{file}), 0, 0700);
158			sysopen my $fh, $self->{file}, O_RDWR \| O_CREAT, 0600
159			or die "$self->{file}: $!\n";
160			flock $fh, LOCK_EX or die "$self->{file}: $!\n";
161			binmode $fh, ":encoding(UTF-8)";
162
163			my $disk = bless { file => $self->{file}, section => {} }, ref $self;
164			$disk->_read ($fh);
165
166			unless (exists $disk->{section}{global}{secret}) {
167			seek $fh, 0, 2 or die "$self->{file}: $!\n";
168			print {$fh} "\n[global]\nsecret = $secret\n"
169			or die "$self->{file}: $!\n";
170			$disk->{section}{global}{secret} = $secret;
171			}
172
173			close $fh or die "$self->{file}: $!\n";
174			$self->{section} = $disk->{section};
175			1
176			} or warn "Cannot save MCP master secret; credentials may only be stable for this process: $@";
177
178			$self->{section}{global}{secret} = $secret
179			unless exists $self->{section}{global}{secret};
180			}
181
182			sub init {
183			my ($class, %kv) = @_;
184			my $file = exists $kv{file} ? $kv{file} : _file;
185
186			my $secret = AnyEvent::MCP::random_bytes 64;
187
188			File::Path::mkpath (File::Basename::dirname ($file), 0, 0700);
189
190			sysopen my $fh, $file, O_WRONLY \| O_CREAT \| O_EXCL, 0600
191			or die "$file: $!\n";
192
193			print {$fh} "[global]\nsecret = ", unpack ("H*", $secret), "\n"
194			or die "$file: $!\n";
195			close $fh or die "$file: $!\n";
196
197			$class->new (file => $file)
198			}
199
200			sub credential {
201			my ($self, $purpose, $name, $username) = @_;
202
203			$username = "" unless defined $username;
204
205			die "Unknown credential purpose '$purpose'\n"
206			unless $purpose =~ /\A(?:basic\|bearer\|cookie)\z/;
207
208			my $secret = $self->{section}{global}{secret};
209			die "$self->{file}: missing or invalid secret\n"
210			unless $secret =~ /\A[0-9a-fA-F]{128}\z/;
211
212			my $info = pack "N/aN/aN/aN/a",
213			"AnyEvent::MCP credential v1", $purpose,
214	root	1.2	AnyEvent::MCP::utf8enc ($name), AnyEvent::MCP::utf8enc ($username);
215	root	1.1
216			my $credential = MIME::Base64::encode_base64 (
217			AnyEvent::MCP::hkdf_sha512_expand (pack ("H*", $secret), $info, 32), ""
218			);
219			$credential =~ y!+/=!-_!d;
220
221			$credential
222			}
223
224			sub url {
225			my ($self, $name, $username) = @_;
226
227			my $url = $self->{section}{"server $name"}{url}
228			or die "No URL configured for server '$name'\n";
229
230			$url =~ s/\{cookie\}/$self->credential ("cookie", $name, $username)/ge;
231
232			$url
233			}
234
235			1