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// Copyright 2015 Matthew Holt and The Caddy Authors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package caddytls
import (
"crypto/tls"
"crypto/x509"
"encoding/json"
"fmt"
"math/big"
"slices"
"github.com/caddyserver/certmagic"
"github.com/caddyserver/caddy/v2/caddyconfig/caddyfile"
)
// CustomCertSelectionPolicy represents a policy for selecting the certificate
// used to complete a handshake when there may be multiple options. All fields
// specified must match the candidate certificate for it to be chosen.
// This was needed to solve https://github.com/caddyserver/caddy/issues/2588.
type CustomCertSelectionPolicy struct {
// The certificate must have one of these serial numbers.
SerialNumber []bigInt `json:"serial_number,omitempty"`
// The certificate must have one of these organization names.
SubjectOrganization []string `json:"subject_organization,omitempty"`
// The certificate must use this public key algorithm.
PublicKeyAlgorithm PublicKeyAlgorithm `json:"public_key_algorithm,omitempty"`
// The certificate must have at least one of the tags in the list.
AnyTag []string `json:"any_tag,omitempty"`
// The certificate must have all of the tags in the list.
AllTags []string `json:"all_tags,omitempty"`
}
// SelectCertificate implements certmagic.CertificateSelector. It
// only chooses a certificate that at least meets the criteria in
// p. It then chooses the first non-expired certificate that is
// compatible with the client. If none are valid, it chooses the
// first viable candidate anyway.
func (p CustomCertSelectionPolicy) SelectCertificate(hello *tls.ClientHelloInfo, choices []certmagic.Certificate) (certmagic.Certificate, error) {
viable := make([]certmagic.Certificate, 0, len(choices))
nextChoice:
for _, cert := range choices {
if len(p.SerialNumber) > 0 {
var found bool
for _, sn := range p.SerialNumber {
snInt := sn.Int // avoid taking address of iteration variable (gosec warning)
if cert.Leaf.SerialNumber.Cmp(&snInt) == 0 {
found = true
break
}
}
if !found {
continue
}
}
if len(p.SubjectOrganization) > 0 {
found := slices.ContainsFunc(p.SubjectOrganization, func(s string) bool {
return slices.Contains(cert.Leaf.Subject.Organization, s)
})
if !found {
continue
}
}
if p.PublicKeyAlgorithm != PublicKeyAlgorithm(x509.UnknownPublicKeyAlgorithm) &&
PublicKeyAlgorithm(cert.Leaf.PublicKeyAlgorithm) != p.PublicKeyAlgorithm {
continue
}
if len(p.AnyTag) > 0 {
var found bool
for _, tag := range p.AnyTag {
if cert.HasTag(tag) {
found = true
break
}
}
if !found {
continue
}
}
if len(p.AllTags) > 0 {
for _, tag := range p.AllTags {
if !cert.HasTag(tag) {
continue nextChoice
}
}
}
// this certificate at least meets the policy's requirements,
// but we still have to check expiration and compatibility
viable = append(viable, cert)
}
if len(viable) == 0 {
return certmagic.Certificate{}, fmt.Errorf("no certificates matched custom selection policy")
}
return certmagic.DefaultCertificateSelector(hello, viable)
}
// UnmarshalCaddyfile sets up the CustomCertSelectionPolicy from Caddyfile tokens. Syntax:
//
// cert_selection {
// all_tags <values...>
// any_tag <values...>
// public_key_algorithm <dsa|ecdsa|rsa>
// serial_number <big_integers...>
// subject_organization <values...>
// }
func (p *CustomCertSelectionPolicy) UnmarshalCaddyfile(d *caddyfile.Dispenser) error {
_, wrapper := d.Next(), d.Val() // consume wrapper name
// No same-line options are supported
if d.CountRemainingArgs() > 0 {
return d.ArgErr()
}
var hasPublicKeyAlgorithm bool
for nesting := d.Nesting(); d.NextBlock(nesting); {
optionName := d.Val()
switch optionName {
case "all_tags":
if d.CountRemainingArgs() == 0 {
return d.ArgErr()
}
p.AllTags = append(p.AllTags, d.RemainingArgs()...)
case "any_tag":
if d.CountRemainingArgs() == 0 {
return d.ArgErr()
}
p.AnyTag = append(p.AnyTag, d.RemainingArgs()...)
case "public_key_algorithm":
if hasPublicKeyAlgorithm {
return d.Errf("duplicate %s option '%s'", wrapper, optionName)
}
if d.CountRemainingArgs() != 1 {
return d.ArgErr()
}
d.NextArg()
if err := p.PublicKeyAlgorithm.UnmarshalJSON([]byte(d.Val())); err != nil {
return d.Errf("parsing %s option '%s': %v", wrapper, optionName, err)
}
hasPublicKeyAlgorithm = true
case "serial_number":
if d.CountRemainingArgs() == 0 {
return d.ArgErr()
}
for d.NextArg() {
val, bi := d.Val(), bigInt{}
_, ok := bi.SetString(val, 10)
if !ok {
return d.Errf("parsing %s option '%s': invalid big.int value %s", wrapper, optionName, val)
}
p.SerialNumber = append(p.SerialNumber, bi)
}
case "subject_organization":
if d.CountRemainingArgs() == 0 {
return d.ArgErr()
}
p.SubjectOrganization = append(p.SubjectOrganization, d.RemainingArgs()...)
default:
return d.ArgErr()
}
// No nested blocks are supported
if d.NextBlock(nesting + 1) {
return d.Errf("malformed %s option '%s': blocks are not supported", wrapper, optionName)
}
}
return nil
}
// bigInt is a big.Int type that interops with JSON encodings as a string.
type bigInt struct{ big.Int }
func (bi bigInt) MarshalJSON() ([]byte, error) {
return json.Marshal(bi.String())
}
func (bi *bigInt) UnmarshalJSON(p []byte) error {
if string(p) == "null" {
return nil
}
var stringRep string
err := json.Unmarshal(p, &stringRep)
if err != nil {
return err
}
_, ok := bi.SetString(stringRep, 10)
if !ok {
return fmt.Errorf("not a valid big integer: %s", p)
}
return nil
}
// Interface guard
var _ caddyfile.Unmarshaler = (*CustomCertSelectionPolicy)(nil)
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