Improve time functions

This PR changes name of the toTime template function to formatTime and
adds toTime and mustToTime, which parse a string and convert it to a time,
and toLayout that converts strings like time.RFC3339 to the actual
layout string.

internal/templates/funcmap.go

@@ -2,6 +2,7 @@ package templates
 
 import (
 	"errors"
+	"strings"
 	"text/template"
 	"time"
 
@@ -10,12 +11,16 @@ import (
 )
 
 // GetFuncMap returns the list of functions provided by sprig. It adds the
-// function "toTime" and changes the function "fail".
+// function "formatTime", "toTime", "mustToTime", and changes the function
+// "fail".
 //
-// The "toTime" function receives a time or a Unix epoch and formats it to
-// RFC3339 in UTC. The "fail" function sets the provided message, so that
-// template errors are reported directly to the template without having the
-// wrapper that text/template adds.
+// The "formatTime" function receives a time or a Unix epoch and formats it to
+// RFC3339 in UTC. The "toTime" and "mustToTime" functions parses a formatted
+// string and returns the time value it represents. The "toLayout" function
+// converts strings like "time.RFC3339" or "time.UnixDate" to the actual layout
+// represented by the Go constant with the same name. The "fail" function sets
+// the provided message, so that template errors are reported directly to the
+// template without having the wrapper that text/template adds.
 //
 // sprig "env" and "expandenv" functions are removed to avoid the leak of
 // information.
@@ -27,11 +32,14 @@ func GetFuncMap(failMessage *string) template.FuncMap {
 		*failMessage = msg
 		return "", errors.New(msg)
 	}
+	m["formatTime"] = formatTime
 	m["toTime"] = toTime
+	m["mustToTime"] = mustToTime
+	m["toLayout"] = toLayout
 	return m
 }
 
-func toTime(v any) string {
+func formatTime(v any) string {
 	var t time.Time
 	switch date := v.(type) {
 	case time.Time:
@@ -55,3 +63,79 @@ func toTime(v any) string {
 	}
 	return t.UTC().Format(time.RFC3339)
 }
+
+func toTime(v ...string) time.Time {
+	t, _ := mustToTime(v...)
+	return t
+}
+
+func mustToTime(v ...string) (time.Time, error) {
+	switch len(v) {
+	case 0:
+		return time.Now().UTC(), nil
+	case 1:
+		return time.Parse(time.RFC3339, v[0])
+	case 2:
+		layout := toLayout(v[0])
+		return time.Parse(layout, v[1])
+	case 3:
+		layout := toLayout(v[0])
+		loc, err := time.LoadLocation(v[2])
+		if err != nil {
+			return time.Time{}, err
+		}
+		return time.ParseInLocation(layout, v[1], loc)
+	default:
+		return time.Time{}, errors.New("unsupported number of parameters")
+	}
+}
+
+func toLayout(fmt string) string {
+	if !strings.HasPrefix(fmt, "time.") {
+		return fmt
+	}
+
+	switch fmt {
+	case "time.Layout":
+		return time.Layout
+	case "time.ANSIC":
+		return time.ANSIC
+	case "time.UnixDate":
+		return time.UnixDate
+	case "time.RubyDate":
+		return time.RubyDate
+	case "time.RFC822":
+		return time.RFC822
+	case "time.RFC822Z":
+		return time.RFC822Z
+	case "time.RFC850":
+		return time.RFC850
+	case "time.RFC1123":
+		return time.RFC1123
+	case "time.RFC1123Z":
+		return time.RFC1123Z
+	case "time.RFC3339":
+		return time.RFC3339
+	case "time.RFC3339Nano":
+		return time.RFC3339Nano
+	// From the ones bellow, only time.DateTime will parse a complete date.
+	case "time.Kitchen":
+		return time.Kitchen
+	case "time.Stamp":
+		return time.Stamp
+	case "time.StampMilli":
+		return time.StampMilli
+	case "time.StampMicro":
+		return time.StampMicro
+	case "time.StampNano":
+		return time.StampNano
+	case "time.DateTime":
+		return time.DateTime
+	case "time.DateOnly":
+		return time.DateOnly
+	case "time.TimeOnly":
+		return time.TimeOnly
+	default:
+		return fmt
+	}
+}

internal/templates/funcmap_test.go

@@ -26,7 +26,7 @@ func Test_GetFuncMap_fail(t *testing.T) {
 	}
 }
 
-func TestGetFuncMap_toTime(t *testing.T) {
+func TestGetFuncMap_formatTime(t *testing.T) {
 	now := time.Now()
 	numericDate := jose.NewNumericDate(now)
 	expected := now.UTC().Format(time.RFC3339)
@@ -57,15 +57,15 @@ func TestGetFuncMap_toTime(t *testing.T) {
 		t.Run(tt.name, func(t *testing.T) {
 			var failMesage string
 			fns := GetFuncMap(&failMesage)
-			fn := fns["toTime"].(func(any) string)
+			fn := fns["formatTime"].(func(any) string)
 			assert.Equal(t, tt.want, fn(tt.args.v))
 		})
 	}
 
 	t.Run("default", func(t *testing.T) {
 		var failMesage string
 		fns := GetFuncMap(&failMesage)
-		fn := fns["toTime"].(func(any) string)
+		fn := fns["formatTime"].(func(any) string)
 		want := time.Now()
 		got, err := time.Parse(time.RFC3339, fn(nil))
 		require.NoError(t, err)

x509util/certificate_test.go

@@ -320,7 +320,7 @@ func TestNewCertificateTemplate(t *testing.T) {
 		(dict "type" "userPrincipalName" "value" .Token.upn)
 		(dict "type" "1.2.3.4" "value" (printf "int:%s" .Insecure.User.id))
 	) | toJson }},
-	"notBefore": "{{ .Token.nbf | toTime }}",
+	"notBefore": "{{ .Token.nbf | formatTime }}",
 	"notAfter": {{ now | dateModify "24h" | toJson }},
 	{{- if typeIs "*rsa.PublicKey" .Insecure.CR.PublicKey }}
 		"keyUsage": ["keyEncipherment", "digitalSignature"],