Config: Can add static headers to email messages (#79365)

* Can add allowed custom headers to an email Message. WIP.

* adds slug as a custom email header to all outgoing emails

* Headers are static - declared as key/value pairs in config. All static headers get added to emails.

* updates comment

* adds tests for parsing smtp static headers

* updates test to assert static headers are included when building email

* updates test to use multiple static headers

* updates test names

* fixes linting issue with error

* ignore gocyclo for loading config

* updates email headers in tests to be formatted properly

* add static headers first

* updates tests to assert that regular headers like From cant be overwritten

* ensures only the header is in a valid format for smtp and not the value

* updates comment and error message wording

* adds to docs and ini sample files

* updates smtp.static_headers docs examples formatting

* removes lines commented with semi colons

* prettier:write

* renames var

pkg/setting/setting.go

@@ -1026,6 +1026,7 @@ func (cfg *Cfg) validateStaticRootPath() error {
 	return nil
 }
 
+// nolint:gocyclo
 func (cfg *Cfg) Load(args CommandLineArgs) error {
 	cfg.setHomePath(args)
 
@@ -1197,7 +1198,9 @@ func (cfg *Cfg) Load(args CommandLineArgs) error {
 	cfg.handleAWSConfig()
 	cfg.readAzureSettings()
 	cfg.readSessionConfig()
-	cfg.readSmtpSettings()
+	if err := cfg.readSmtpSettings(); err != nil {
+		return err
+	}
 	if err := cfg.readAnnotationSettings(); err != nil {
 		return err
 	}

pkg/setting/setting_smtp.go

@@ -1,6 +1,11 @@
 package setting
 
-import "github.com/grafana/grafana/pkg/util"
+import (
+	"fmt"
+	"regexp"
+
+	"github.com/grafana/grafana/pkg/util"
+)
 
 type SmtpSettings struct {
 	Enabled        bool
@@ -14,13 +19,17 @@ type SmtpSettings struct {
 	EhloIdentity   string
 	StartTLSPolicy string
 	SkipVerify     bool
+	StaticHeaders  map[string]string
 
 	SendWelcomeEmailOnSignUp bool
 	TemplatesPatterns        []string
 	ContentTypes             []string
 }
 
-func (cfg *Cfg) readSmtpSettings() {
+// validates mail headers
+var mailHeaderRegex = regexp.MustCompile(`^[A-Z][A-Za-z0-9]*(-[A-Z][A-Za-z0-9]*)*$`)
+
+func (cfg *Cfg) readSmtpSettings() error {
 	sec := cfg.Raw.Section("smtp")
 	cfg.Smtp.Enabled = sec.Key("enabled").MustBool(false)
 	cfg.Smtp.Host = sec.Key("host").String()
@@ -38,4 +47,31 @@ func (cfg *Cfg) readSmtpSettings() {
 	cfg.Smtp.SendWelcomeEmailOnSignUp = emails.Key("welcome_email_on_sign_up").MustBool(false)
 	cfg.Smtp.TemplatesPatterns = util.SplitString(emails.Key("templates_pattern").MustString("emails/*.html, emails/*.txt"))
 	cfg.Smtp.ContentTypes = util.SplitString(emails.Key("content_types").MustString("text/html"))
+
+	// populate static headers
+	if err := cfg.readGrafanaSmtpStaticHeaders(); err != nil {
+		return err
+	}
+
+	return nil
+}
+
+func validHeader(header string) bool {
+	return mailHeaderRegex.MatchString(header)
+}
+
+func (cfg *Cfg) readGrafanaSmtpStaticHeaders() error {
+	staticHeadersSection := cfg.Raw.Section("smtp.static_headers")
+	keys := staticHeadersSection.Keys()
+	cfg.Smtp.StaticHeaders = make(map[string]string, len(keys))
+
+	for _, key := range keys {
+		if !validHeader(key.Name()) {
+			return fmt.Errorf("header %q in [smtp.static_headers] configuration: must follow canonical MIME form", key.Name())
+		}
+
+		cfg.Smtp.StaticHeaders[key.Name()] = key.Value()
+	}
+
+	return nil
 }

pkg/setting/setting_smtp_test.go

@@ -0,0 +1,93 @@
+package setting
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+	"gopkg.in/ini.v1"
+)
+
+func TestLoadSmtpStaticHeaders(t *testing.T) {
+	t.Run("will load valid headers", func(t *testing.T) {
+		f := ini.Empty()
+		cfg := NewCfg()
+		s, err := f.NewSection("smtp.static_headers")
+		require.NoError(t, err)
+		cfg.Raw = f
+		_, err = s.NewKey("Foo-Header", "foo_val")
+		require.NoError(t, err)
+		_, err = s.NewKey("Bar", "bar_val")
+		require.NoError(t, err)
+
+		err = cfg.readGrafanaSmtpStaticHeaders()
+		require.NoError(t, err)
+
+		assert.Equal(t, "foo_val", cfg.Smtp.StaticHeaders["Foo-Header"])
+		assert.Equal(t, "bar_val", cfg.Smtp.StaticHeaders["Bar"])
+	})
+
+	t.Run("will load no static headers into smtp config when section is defined but has no keys", func(t *testing.T) {
+		f := ini.Empty()
+		cfg := NewCfg()
+		_, err := f.NewSection("smtp.static_headers")
+		require.NoError(t, err)
+		cfg.Raw = f
+
+		err = cfg.readGrafanaSmtpStaticHeaders()
+		require.NoError(t, err)
+
+		assert.Empty(t, cfg.Smtp.StaticHeaders)
+	})
+
+	t.Run("will load no static headers into smtp config when section is not defined", func(t *testing.T) {
+		f := ini.Empty()
+		cfg := NewCfg()
+		cfg.Raw = f
+
+		err := cfg.readGrafanaSmtpStaticHeaders()
+		require.NoError(t, err)
+
+		assert.Empty(t, cfg.Smtp.StaticHeaders)
+	})
+
+	t.Run("will return error when header label is not in valid format", func(t *testing.T) {
+		f := ini.Empty()
+		cfg := NewCfg()
+		s, err := f.NewSection("smtp.static_headers")
+		require.NoError(t, err)
+		_, err = s.NewKey("header with spaces", "value")
+		require.NoError(t, err)
+		cfg.Raw = f
+
+		err = cfg.readGrafanaSmtpStaticHeaders()
+		require.Error(t, err)
+	})
+}
+
+func TestSmtpHeaderValidation(t *testing.T) {
+	testCases := []struct {
+		input    string
+		expected bool
+	}{
+		//valid
+		{"Foo", true},
+		{"Foo-Bar", true},
+		{"Foo123-Bar123", true},
+
+		//invalid
+		{"foo", false},
+		{"Foo Bar", false},
+		{"123Foo", false},
+		{"Foo.Bar", false},
+		{"foo-bar", false},
+		{"foo-Bar", false},
+		{"Foo-bar", false},
+		{"-Bar", false},
+		{"Foo--", false},
+	}
+
+	for _, tc := range testCases {
+		assert.Equal(t, validHeader(tc.input), tc.expected)
+	}
+}