feat: add initial implementation of osiris, the TLS terminator for Anubis

Signed-off-by: Xe Iaso <me@xeiaso.net>

cmd/osiris/internal/config/tls.go

@@ -0,0 +1,40 @@
+package config
+
+import (
+	"crypto/tls"
+	"errors"
+	"fmt"
+	"os"
+)
+
+var (
+	ErrCantReadTLS       = errors.New("tls: can't read TLS")
+	ErrInvalidTLSKeypair = errors.New("tls: can't parse TLS keypair")
+)
+
+type TLS struct {
+	Cert string `hcl:"cert"`
+	Key  string `hcl:"key"`
+}
+
+func (t TLS) Valid() error {
+	var errs []error
+
+	if _, err := os.Stat(t.Cert); err != nil {
+		errs = append(errs, fmt.Errorf("%w certificate %s: %w", ErrCantReadTLS, t.Cert, err))
+	}
+
+	if _, err := os.Stat(t.Key); err != nil {
+		errs = append(errs, fmt.Errorf("%w key %s: %w", ErrCantReadTLS, t.Key, err))
+	}
+
+	if _, err := tls.LoadX509KeyPair(t.Cert, t.Key); err != nil {
+		errs = append(errs, fmt.Errorf("%w (%s, %s): %w", ErrInvalidTLSKeypair, t.Cert, t.Key, err))
+	}
+
+	if len(errs) != 0 {
+		return errors.Join(errs...)
+	}
+
+	return nil
+}