authenticate/proxy: add backend refresh (#438)

internal/sessions/header/header_store.go

@@ -0,0 +1,64 @@
+package header // import "github.com/pomerium/pomerium/internal/sessions/header"
+
+import (
+	"net/http"
+	"strings"
+
+	"github.com/pomerium/pomerium/internal/encoding"
+	"github.com/pomerium/pomerium/internal/sessions"
+)
+
+var _ sessions.SessionLoader = &Store{}
+
+const (
+	defaultAuthHeader = "Authorization"
+	defaultAuthType   = "Bearer"
+)
+
+// Store implements the load session store interface using http
+// authorization headers.
+type Store struct {
+	authHeader string
+	authType   string
+	encoder    encoding.Unmarshaler
+}
+
+// NewStore returns a new header store for loading sessions from
+// authorization header as defined in as defined in rfc2617
+//
+// NOTA BENE: While most servers do not log Authorization headers by default,
+// you should ensure no other services are logging or leaking your auth headers.
+func NewStore(enc encoding.Unmarshaler, headerType string) *Store {
+	if headerType == "" {
+		headerType = defaultAuthType
+	}
+	return &Store{
+		authHeader: defaultAuthHeader,
+		authType:   headerType,
+		encoder:    enc,
+	}
+}
+
+// LoadSession tries to retrieve the token string from the Authorization header.
+func (as *Store) LoadSession(r *http.Request) (*sessions.State, error) {
+	cipherText := TokenFromHeader(r, as.authHeader, as.authType)
+	if cipherText == "" {
+		return nil, sessions.ErrNoSessionFound
+	}
+	var session sessions.State
+	if err := as.encoder.Unmarshal([]byte(cipherText), &session); err != nil {
+		return nil, sessions.ErrMalformed
+	}
+	return &session, nil
+}
+
+// TokenFromHeader retrieves the value of the authorization header from a given
+// request, header key, and authentication type.
+func TokenFromHeader(r *http.Request, authHeader, authType string) string {
+	bearer := r.Header.Get(authHeader)
+	atSize := len(authType)
+	if len(bearer) > atSize && strings.EqualFold(bearer[0:atSize], authType) {
+		return bearer[atSize+1:]
+	}
+	return ""
+}