feat: Support host + path based routing

Create StateFunc type with relativeURL + schemeAndHost strategies for
forwarding requests. The value of SESSION_DOMAIN is used to pick the
strategy. If SESSION_DOMAIN is set then AuthService will be able to
serve requests for all subdomains of SESSION_DOMAIN and the host + path
of the request will be used when saving the oidc state for the request.

This commit adds 2 new env vars:
2. SCHEME_DEFAULT - default request scheme
3. SCHEME_HEADER - header to get original request scheme from

README.md

@@ -98,7 +98,9 @@ Session store-related settings:
 | `OIDC_STATE_STORE_PATH` | "/var/lib/authservice/oidc_state.db" | Path to the session store used to save the sessions for the OIDC state parameter. |
 | `SESSION_MAX_AGE` | "86400" | Time in seconds after which sessions expire. Defaults to a day (24h). |
 | `SESSION_SAME_SITE` | "Lax" | SameSite attribute of the session cookie. Check details of SameSite attribute [here](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Set-Cookie/SameSite). Its value can be "None", "Lax" or "Strict". |
-| `SESSION_DOMAIN` | "" | Domain attribute of the session cookie. Check details of Domain attribute [here](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Set-Cookie)  |
+| `SESSION_DOMAIN` | "" | Domain attribute of the session cookie. Check details of Domain attribute [here](https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/Set-Cookie). If len(SESSION_DOMAIN) > 0 the incoming request's host and scheme are also saved in the state rather than just the path. This enables AuthService to service all subdomains of SESSION_DOMAIN. |
+| `SCHEME_DEFAULT` | `https` | Default scheme for incoming requests. |
+| `SCHEME_HEADER` | `<empty>` | Header to use for incoming request scheme. If ommitted or header is not present in request, SCHEME_DEFAULT will be used instead. |
 
 By default, the AuthService keeps sessions to check if a user is authenticated. However, there may be times where
 we want to check a user's logged in status at the Provider, effectively making the Provider the one keeping the

main.go

@@ -161,6 +161,7 @@ func main() {
 		// TODO: Add support for Redis
 		store:                  store,
 		oidcStateStore:         oidcStateStore,
+		stateFunc:              NewStateFunc(c),
 		afterLoginRedirectURL:  c.AfterLoginURL.String(),
 		homepageURL:            c.HomepageURL.String(),
 		afterLogoutRedirectURL: c.AfterLogoutURL.String(),

server.go

@@ -47,6 +47,7 @@ type server struct {
 	upstreamHTTPHeaderOpts  httpHeaderOpts
 	caBundle                []byte
 	sessionSameSite         http.SameSite
+	stateFunc               StateFunc
 }
 
 // jwtClaimOpts specifies the location of the user's identity inside a JWT's
@@ -142,7 +143,7 @@ func (s *server) authCodeFlowAuthenticationRequest(w http.ResponseWriter, r *htt
 	logger := loggerForRequest(r)
 
 	// Initiate OIDC Flow with Authorization Request.
-	state, err := createState(r, w, s.oidcStateStore)
+	state, err := createState(r, w, s.oidcStateStore, s.stateFunc)
 	if err != nil {
 		logger.Errorf("Failed to save state in store: %v", err)
 		returnMessage(w, http.StatusInternalServerError, "Failed to save state in store.")

state.go

@@ -5,10 +5,12 @@ package main
 import (
 	"encoding/gob"
 	"net/http"
+	"strings"
 	"time"
 
 	"github.com/gorilla/sessions"
 	"github.com/pkg/errors"
+	log "github.com/sirupsen/logrus"
 )
 
 const (
@@ -20,6 +22,13 @@ func init() {
 	gob.Register(State{})
 }
 
+// TODO move state code to its own package
+// type Config struct {
+// 	SchemeDefault string
+// 	SchemeHeader  string
+// 	SessionDomain string
+// }
+
 type State struct {
 	// FirstVisitedURL is the URL that the user visited when we redirected them
 	// to login.
@@ -32,14 +41,46 @@ func newState(firstVisitedURL string) *State {
 	}
 }
 
+type StateFunc func(*http.Request) *State
+
+func NewStateFunc(config *config) StateFunc {
+	if len(config.SessionDomain) > 0 {
+		return newSchemeAndHost(config)
+	}
+	return relativeURL
+}
+
+func relativeURL(r *http.Request) *State {
+	return &state{
+		FirstVisitedURL: r.URL.String(),
+	}
+}
+
+func newSchemeAndHost(config *config) StateFunc {
+	return func(r *http.Request) *State {
+		// Use header value if it exists
+		s := r.Header.Get(config.SchemeHeader)
+		if s == "" {
+			s = config.SchemeDefault
+		}
+		// XXX Could return an error here. Would require changing the StateFunc type
+		if !strings.HasSuffix(r.Host, config.SessionDomain) {
+			log.Warnf("Request host %q is not a subdomain of %q", r.Host, config.SessionDomain)
+		}
+		return &state{
+			FirstVisitedURL: s + "://" + r.Host + r.URL.String(),
+		}
+	}
+}
+
 // createState creates the state parameter from the incoming request, stores
 // it in the session store and sets a cookie with the session key.
 // It returns the session key, which can be used as the state value to start
 // an OIDC authentication request.
 func createState(r *http.Request, w http.ResponseWriter,
-	store sessions.Store) (string, error) {
+	store sessions.Store, sf StateFunc) (string, error) {
 
-	s := newState(r.URL.Path)
+	s := sf(r.URL.Path)
 	session := sessions.NewSession(store, oidcStateCookie)
 	session.Options.MaxAge = int(20 * time.Minute)
 	session.Values[sessionValueState] = *s