Client certificate for relay

Bumps [github/codeql-action](https://github.com/github/codeql-action) from 4.31.9 to 4.31.10.
- [Release notes](https://github.com/github/codeql-action/releases)
- [Changelog](https://github.com/github/codeql-action/blob/main/CHANGELOG.md)
- [Commits](5d4e8d1aca...cdefb33c0f)

---
updated-dependencies:
- dependency-name: github/codeql-action
  dependency-version: 4.31.10
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

Signed-off-by: dependabot[bot] <support@github.com>

.github/workflows/codeql-analysis.yml

@@ -47,7 +47,7 @@ jobs:
 
     # Initializes the CodeQL tools for scanning.
     - name: Initialize CodeQL
-      uses: github/codeql-action/init@5d4e8d1aca955e8d8589aabd499c5cae939e33c7 # v4.31.9
+      uses: github/codeql-action/init@cdefb33c0f6224e58673d9004f47f7cb3e328b89 # v4.31.10
       with:
         languages: ${{ matrix.language }}
         # If you wish to specify custom queries, you can do so here or in a config file.
@@ -58,7 +58,7 @@ jobs:
     # Autobuild attempts to build any compiled languages  (C/C++, C#, or Java).
     # If this step fails, then you should remove it and run the build manually (see below)
     - name: Autobuild
-      uses: github/codeql-action/autobuild@5d4e8d1aca955e8d8589aabd499c5cae939e33c7 # v4.31.9
+      uses: github/codeql-action/autobuild@cdefb33c0f6224e58673d9004f47f7cb3e328b89 # v4.31.10
 
     # ℹ️ Command-line programs to run using the OS shell.
     # 📚 https://git.io/JvXDl
@@ -72,4 +72,4 @@ jobs:
     #   make release
 
     - name: Perform CodeQL Analysis
-      uses: github/codeql-action/analyze@5d4e8d1aca955e8d8589aabd499c5cae939e33c7 # v4.31.9
+      uses: github/codeql-action/analyze@cdefb33c0f6224e58673d9004f47f7cb3e328b89 # v4.31.10

.github/workflows/go.yml

@@ -15,7 +15,7 @@ jobs:
         egress-policy: audit
 
     - uses: actions/checkout@8e8c483db84b4bee98b60c0593521ed34d9990e8 # v6.0.1
-    - uses: actions/setup-go@4dc6199c7b1a012772edbd06daecab0f50c9053c # v6.1.0
+    - uses: actions/setup-go@7a3fe6cf4cb3a834922a1244abfce67bcef6a0c5 # v6.2.0
       with:
         go-version: 'stable'
 

.github/workflows/release.yaml

@@ -3,6 +3,12 @@ name: Release Go Binaries
 on:
   release:
     types: [created]
+  workflow_dispatch:
+    inputs:
+      release_tag:
+        description: 'Tag name to build (v1.3.1)'
+        required: false
+        default: ''
 
 # Declare default permissions as read only.
 permissions: read-all
@@ -25,10 +31,25 @@ jobs:
       with:
         egress-policy: audit
 
+    - name: Determine ref to checkout
+      run: |
+        # If manually invoked with a release_tag input, use refs/tags/<release_tag>.
+        if [ "${{ github.event_name }}" = "workflow_dispatch" ] && [ -n "${{ github.event.inputs.release_tag }}" ]; then
+          echo "REF=refs/tags/${{ github.event.inputs.release_tag }}" >> $GITHUB_ENV
+        else
+          # For release events GITHUB_REF is already refs/tags/<tag>; otherwise fall back to the incoming ref.
+          echo "REF=${GITHUB_REF}" >> $GITHUB_ENV
+        fi
+
     - uses: actions/checkout@8e8c483db84b4bee98b60c0593521ed34d9990e8 # v6.0.1
+      with:
+        ref: ${{ env.REF }}
 
     - name: Set APP_VERSION env
-      run: echo APP_VERSION=$(echo ${GITHUB_REF} | rev | cut -d'/' -f 1 | rev ) >> ${GITHUB_ENV}
+      run: |
+        # basename strips refs/... and yields the tag or branch name
+        echo "APP_VERSION=$(basename ${REF})" >> $GITHUB_ENV
+
     - name: Set BUILD_TIME env
       run: echo BUILD_TIME=$(date) >> ${GITHUB_ENV}
       
@@ -39,3 +60,4 @@ jobs:
         goarch: ${{ matrix.goarch }}
         extra_files: LICENSE README.md smtprelay.ini
         ldflags: -s -w -X "main.appVersion=${{ env.APP_VERSION }}" -X "main.buildTime=${{ env.BUILD_TIME }}"
+        release_tag: ${{ env.APP_VERSION }}

.github/workflows/scorecards.yml

@@ -76,6 +76,6 @@ jobs:
 
       # Upload the results to GitHub's code scanning dashboard.
       - name: "Upload to code-scanning"
-        uses: github/codeql-action/upload-sarif@5d4e8d1aca955e8d8589aabd499c5cae939e33c7 # v4.31.9
+        uses: github/codeql-action/upload-sarif@cdefb33c0f6224e58673d9004f47f7cb3e328b89 # v4.31.10
         with:
           sarif_file: results.sarif

config.go

@@ -46,6 +46,8 @@ var (
 	command          = flagset.String("command", "", "Path to pipe command")
 	remotesStr       = flagset.String("remotes", "", "Outgoing SMTP servers")
 	strictSender     = flagset.Bool("strict_sender", false, "Use only SMTP servers with Sender matches to From")
+	remoteCert       = flagset.String("remote_certificate", "", "Client SSL certificate for remote STARTTLS/TLS")
+	remoteKey        = flagset.String("remote_key", "", "Client SSL private key for remote STARTTLS/TLS")
 
 	// additional flags
 	_           = flagset.String("config", "", "Path to config file (ini format)")
@@ -67,6 +69,36 @@ func localAuthRequired() bool {
 	return *allowedUsers != ""
 }
 
+func remoteCertAndKeyReadable() bool {
+	certSet := *remoteCert != ""
+	keySet := *remoteKey != ""
+	
+	// Both must be set or both must be unset
+	if certSet != keySet {
+		return false
+	}
+	
+	// If both are set, verify files exist and are accessible
+	if certSet && keySet {
+		if _, err := os.Stat(*remoteCert); err != nil {
+			log.Error().
+				Str("cert", *remoteCert).
+				Err(err).
+				Msg("cannot access remote client certificate file")
+			return false
+		}
+		if _, err := os.Stat(*remoteKey); err != nil {
+			log.Error().
+				Str("key", *remoteKey).
+				Err(err).
+				Msg("cannot access remote client key file")
+			return false
+		}
+	}
+	
+	return true
+}
+
 func setupAliases() {
 	if *aliasFile != "" {
 		aliases, err := AliasLoadFile(*aliasFile)
@@ -137,6 +169,11 @@ func setupRemotes() {
 				logger.Fatal().Msg(fmt.Sprintf("error parsing url: '%s': %v", remoteURL, err))
 			}
 
+			if *remoteCert != "" && *remoteKey != "" && (r.Scheme == "smtps" || r.Scheme == "starttls") {
+				r.ClientCertPath = *remoteCert
+				r.ClientKeyPath = *remoteKey
+			}
+
 			remotes = append(remotes, r)
 		}
 	}
@@ -253,6 +290,13 @@ func ConfigLoad() {
 		log.Warn().Msg("no remotes or command set; mail will not be forwarded!")
 	}
 
+	if !remoteCertAndKeyReadable() {
+		log.Fatal().
+			Str("remote_certificate", *remoteCert).
+			Str("remote_key", *remoteKey).
+			Msg("remote_certificate and remote_key must both be set or both be empty")
+	}
+
 	setupAllowedNetworks()
 	setupAllowedPatterns()
 	setupAliases()

go.mod

@@ -8,7 +8,7 @@ require (
 	github.com/peterbourgon/ff/v3 v3.4.0
 	github.com/rs/zerolog v1.34.0
 	github.com/stretchr/testify v1.11.1
-	golang.org/x/crypto v0.46.0
+	golang.org/x/crypto v0.47.0
 )
 
 require (
@@ -17,7 +17,7 @@ require (
 	github.com/mattn/go-colorable v0.1.14 // indirect
 	github.com/mattn/go-isatty v0.0.20 // indirect
 	github.com/pmezard/go-difflib v1.0.0 // indirect
-	golang.org/x/sys v0.39.0 // indirect
+	golang.org/x/sys v0.40.0 // indirect
 	gopkg.in/yaml.v3 v3.0.1 // indirect
 )
 

go.sum

@@ -31,13 +31,13 @@ github.com/rs/zerolog v1.34.0 h1:k43nTLIwcTVQAncfCw4KZ2VY6ukYoZaBPNOE8txlOeY=
 github.com/rs/zerolog v1.34.0/go.mod h1:bJsvje4Z08ROH4Nhs5iH600c3IkWhwp44iRc54W6wYQ=
 github.com/stretchr/testify v1.11.1 h1:7s2iGBzp5EwR7/aIZr8ao5+dra3wiQyKjjFuvgVKu7U=
 github.com/stretchr/testify v1.11.1/go.mod h1:wZwfW3scLgRK+23gO65QZefKpKQRnfz6sD981Nm4B6U=
-golang.org/x/crypto v0.46.0 h1:cKRW/pmt1pKAfetfu+RCEvjvZkA9RimPbh7bhFjGVBU=
-golang.org/x/crypto v0.46.0/go.mod h1:Evb/oLKmMraqjZ2iQTwDwvCtJkczlDuTmdJXoZVzqU0=
+golang.org/x/crypto v0.47.0 h1:V6e3FRj+n4dbpw86FJ8Fv7XVOql7TEwpHapKoMJ/GO8=
+golang.org/x/crypto v0.47.0/go.mod h1:ff3Y9VzzKbwSSEzWqJsJVBnWmRwRSHt/6Op5n9bQc4A=
 golang.org/x/sys v0.0.0-20220811171246-fbc7d0a398ab/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.6.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
 golang.org/x/sys v0.12.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
-golang.org/x/sys v0.39.0 h1:CvCKL8MeisomCi6qNZ+wbb0DN9E5AATixKsvNtMoMFk=
-golang.org/x/sys v0.39.0/go.mod h1:OgkHotnGiDImocRcuBABYBEXf8A9a87e/uXjp9XT3ks=
+golang.org/x/sys v0.40.0 h1:DBZZqJ2Rkml6QMQsZywtnjnnGvHza6BTfYFWY9kjEWQ=
+golang.org/x/sys v0.40.0/go.mod h1:OgkHotnGiDImocRcuBABYBEXf8A9a87e/uXjp9XT3ks=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405 h1:yhCVgyC4o1eVCa2tZl7eS0r+SDo693bJlVdllGtEeKM=
 gopkg.in/check.v1 v0.0.0-20161208181325-20d25e280405/go.mod h1:Co6ibVJAznAaIkqp8huTwlJQCZ016jof/cbN4VW5Yz0=
 gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=

remotes.go

@@ -14,6 +14,8 @@ type Remote struct {
 	Port            string
 	Addr            string
 	Sender          string
+	ClientCertPath  string
+	ClientKeyPath   string
 }
 
 // ParseRemote creates a remote from a given url in the following format:

smtp.go

@@ -340,6 +340,14 @@ func SendMail(r *Remote, from string, to []string, msg []byte) error {
 			ServerName:         r.Hostname,
 			InsecureSkipVerify: r.SkipVerify,
 		}
+		// Load client certificate on-demand, just before connection
+		if r.ClientCertPath != "" && r.ClientKeyPath != "" {
+			cert, err := tls.LoadX509KeyPair(r.ClientCertPath, r.ClientKeyPath)
+			if err != nil {
+				return err
+			}
+			config.Certificates = []tls.Certificate{cert}
+		}
 		conn, err := tls.Dial("tcp", r.Addr, config)
 		if err != nil {
 			return err
@@ -366,6 +374,14 @@ func SendMail(r *Remote, from string, to []string, msg []byte) error {
 				ServerName:         c.serverName,
 				InsecureSkipVerify: r.SkipVerify,
 			}
+			// Load client certificate on-demand, just before use
+			if r.ClientCertPath != "" && r.ClientKeyPath != "" {
+				cert, err := tls.LoadX509KeyPair(r.ClientCertPath, r.ClientKeyPath)
+				if err != nil {
+					return err
+				}
+				config.Certificates = []tls.Certificate{cert}
+			}
 			if testHookStartTLS != nil {
 				testHookStartTLS(config)
 			}

smtprelay.ini

@@ -119,6 +119,10 @@
 ; Mailjet.com
 ;remotes = starttls://user:pass@in-v3.mailjet.com:587
 
+; Exchange Online (O365) SMTP relay
+; (Change netloc to your own Exchange MX endpoint)
+; remotes = starttls://contoso-com.mail.protection.outlook.com:25
+
 ; Ignore remote host certificates
 ;remotes = starttls://user:pass@server:587?skipVerify
 
@@ -131,5 +135,11 @@
 ; Multiple remotes, space delimited
 ;remotes = smtp://127.0.0.1:1025 starttls://user:pass@smtp.mailgun.org:587
 
+; Client SSL certificate for remote STARTTLS/TLS
+; remote_certificate = /path/to/certificate-chain.pem
+
+; Client SSL private key for remote STARTTLS/TLS
+; remote_key = /path/to/private-key.pem
+
 ; Pipe messages to external command
 ;command = /usr/local/bin/script