proxy(router): Allow to set some outgoing headers

This introduces the "additional_headers", "remote_user_header" and
"skip_x_access_token" config keys to allow configuring routes to
external services that require addtional headers to be set.

"remote_user_header": defines the name of a Header that will carry the
userid of the authenticated user on the outgoing request.

"additional_headers": defines a list of header names and values that will
be added to outgoing requests on matching routes.

"skip_x_access_token": when set to true the reva access token will not
be added to the outgoing request.

Needed for #206

services/proxy/pkg/middleware/account_resolver.go

@@ -7,6 +7,7 @@ import (
 	"time"
 
 	"github.com/jellydator/ttlcache/v3"
+	"github.com/opencloud-eu/opencloud/services/proxy/pkg/router"
 	"github.com/opencloud-eu/opencloud/services/proxy/pkg/user/backend"
 	"github.com/opencloud-eu/opencloud/services/proxy/pkg/userroles"
 
@@ -209,7 +210,13 @@ func (m accountResolver) ServeHTTP(w http.ResponseWriter, req *http.Request) {
 		}
 	}
 
-	req.Header.Set(revactx.TokenHeader, token)
+	ri := router.ContextRoutingInfo(ctx)
+	if ri.RemoteUserHeader() != "" {
+		req.Header.Set(ri.RemoteUserHeader(), user.GetId().GetOpaqueId())
+	}
+	if !ri.SkipXAccessToken() {
+		req.Header.Set(revactx.TokenHeader, token)
+	}
 
 	m.next.ServeHTTP(w, req)
 }

services/proxy/pkg/middleware/account_resolver_test.go

@@ -9,6 +9,7 @@ import (
 	userv1beta1 "github.com/cs3org/go-cs3apis/cs3/identity/user/v1beta1"
 	"github.com/opencloud-eu/opencloud/pkg/log"
 	"github.com/opencloud-eu/opencloud/pkg/oidc"
+	"github.com/opencloud-eu/opencloud/services/proxy/pkg/router"
 	"github.com/opencloud-eu/opencloud/services/proxy/pkg/user/backend"
 	"github.com/opencloud-eu/opencloud/services/proxy/pkg/user/backend/mocks"
 	userRoleMocks "github.com/opencloud-eu/opencloud/services/proxy/pkg/userroles/mocks"
@@ -206,6 +207,7 @@ func mockRequest(claims map[string]interface{}) (*http.Request, *httptest.Respon
 	}
 
 	ctx := oidc.NewContext(context.Background(), claims)
+	ctx = router.SetRoutingInfo(ctx, router.RoutingInfo{})
 	req := httptest.NewRequest("GET", "http://example.com/foo", nil).WithContext(ctx)
 	rw := httptest.NewRecorder()