diff --git a/authorize/evaluator/evaluator.go b/authorize/evaluator/evaluator.go
index e0d5b7026..b6ebe7c58 100644
--- a/authorize/evaluator/evaluator.go
+++ b/authorize/evaluator/evaluator.go
@@ -292,6 +292,7 @@ var internalPathsNeedingLogin = set.From([]string{
 	"/.pomerium/webauthn",
 	"/.pomerium/routes",
 	"/.pomerium/api/v1/routes",
+	"/.pomerium/mcp/authorize",
 })
 
 func (e *Evaluator) evaluateInternal(_ context.Context, req *Request) (*PolicyResponse, error) {
diff --git a/go.mod b/go.mod
index 27484a601..db043331d 100644
--- a/go.mod
+++ b/go.mod
@@ -71,7 +71,6 @@ require (
 	github.com/tniswong/go.rfcx v0.0.0-20181019234604-07783c52761f
 	github.com/volatiletech/null/v9 v9.0.0
 	github.com/yuin/gopher-lua v1.1.1
-	github.com/zeebo/assert v1.3.1
 	github.com/zeebo/xxh3 v1.0.2
 	go.opencensus.io v0.24.0
 	go.opentelemetry.io/contrib/instrumentation/google.golang.org/grpc/otelgrpc v0.60.0
@@ -233,6 +232,7 @@ require (
 	github.com/xeipuuv/gojsonreference v0.0.0-20180127040603-bd5ef7bd5415 // indirect
 	github.com/yashtewari/glob-intersection v0.2.0 // indirect
 	github.com/yusufpapurcu/wmi v1.2.4 // indirect
+	github.com/zeebo/assert v1.3.1 // indirect
 	github.com/zeebo/blake3 v0.2.4 // indirect
 	go.opentelemetry.io/auto/sdk v1.1.0 // indirect
 	go.opentelemetry.io/contrib/detectors/gcp v1.34.0 // indirect
diff --git a/internal/mcp/handler_authorization.go b/internal/mcp/handler_authorization.go
index 2fd667ffb..0021d904e 100644
--- a/internal/mcp/handler_authorization.go
+++ b/internal/mcp/handler_authorization.go
@@ -3,13 +3,16 @@ package mcp
 import (
 	"context"
 	"errors"
+	"fmt"
 	"net/http"
 	"net/url"
 	"time"
 
+	"github.com/go-jose/go-jose/v3/jwt"
 	"google.golang.org/grpc/codes"
 	"google.golang.org/grpc/status"
 
+	"github.com/pomerium/pomerium/internal/httputil"
 	"github.com/pomerium/pomerium/internal/log"
 	"github.com/pomerium/pomerium/internal/oauth21"
 	oauth21proto "github.com/pomerium/pomerium/internal/oauth21/gen"
@@ -24,7 +27,14 @@ func (srv *Handler) Authorize(w http.ResponseWriter, r *http.Request) {
 
 	ctx := r.Context()
 
-	v, err := oauth21.ParseCodeGrantAuthorizeRequest(r)
+	sessionID, err := getSessionFromRequest(r)
+	if err != nil {
+		log.Ctx(ctx).Error().Err(err).Msg("session is not present, this is a misconfigured request")
+		http.Error(w, "internal server error", http.StatusInternalServerError)
+		return
+	}
+
+	v, err := oauth21.ParseCodeGrantAuthorizeRequest(r, sessionID)
 	if err != nil {
 		log.Ctx(ctx).Error().Err(err).Msg("failed to parse authorization request")
 		oauth21.ErrorResponse(w, http.StatusBadRequest, oauth21.InvalidRequest)
@@ -94,3 +104,23 @@ func (srv *Handler) AuthorizationResponse(
 	to.RawQuery = q.Encode()
 	http.Redirect(w, r, to.String(), http.StatusFound)
 }
+
+func getSessionFromRequest(r *http.Request) (string, error) {
+	h := r.Header.Get(httputil.HeaderPomeriumJWTAssertion)
+	if h == "" {
+		return "", fmt.Errorf("missing %s header", httputil.HeaderPomeriumJWTAssertion)
+	}
+
+	token, err := jwt.ParseSigned(h)
+	if err != nil {
+		return "", fmt.Errorf("failed to parse JWT: %w", err)
+	}
+	var m map[string]any
+	_ = token.UnsafeClaimsWithoutVerification(&m)
+	sessionID, ok := m["sid"].(string)
+	if !ok {
+		return "", fmt.Errorf("missing session ID in JWT")
+	}
+
+	return sessionID, nil
+}
diff --git a/internal/oauth21/authorize.go b/internal/oauth21/authorize.go
index fce6aceb0..bd0fc0d4d 100644
--- a/internal/oauth21/authorize.go
+++ b/internal/oauth21/authorize.go
@@ -12,7 +12,7 @@ import (
 // ParseCodeGrantAuthorizeRequest parses the authorization request for the code grant flow.
 // see https://datatracker.ietf.org/doc/html/draft-ietf-oauth-v2-1-12#section-4.1.1
 // scopes are ignored
-func ParseCodeGrantAuthorizeRequest(r *http.Request) (*gen.AuthorizationRequest, error) {
+func ParseCodeGrantAuthorizeRequest(r *http.Request, sessionID string) (*gen.AuthorizationRequest, error) {
 	if err := r.ParseForm(); err != nil {
 		return nil, fmt.Errorf("failed to parse form: %w", err)
 	}
@@ -24,6 +24,7 @@ func ParseCodeGrantAuthorizeRequest(r *http.Request) (*gen.AuthorizationRequest,
 		State:               optionalFormParam(r, "state"),
 		CodeChallenge:       r.Form.Get("code_challenge"),
 		CodeChallengeMethod: optionalFormParam(r, "code_challenge_method"),
+		SessionId:           sessionID,
 	}
 
 	if err := protovalidate.Validate(v); err != nil {
diff --git a/internal/oauth21/gen/authorization_request.pb.go b/internal/oauth21/gen/authorization_request.pb.go
index 756e88042..5f465c9e7 100644
--- a/internal/oauth21/gen/authorization_request.pb.go
+++ b/internal/oauth21/gen/authorization_request.pb.go
@@ -48,8 +48,11 @@ type AuthorizationRequest struct {
 	// OPTIONAL, defaults to plain if not present in the request. Code verifier
 	// transformation method is S256 or plain.
 	CodeChallengeMethod *string `protobuf:"bytes,7,opt,name=code_challenge_method,json=codeChallengeMethod,proto3,oneof" json:"code_challenge_method,omitempty"`
-	unknownFields       protoimpl.UnknownFields
-	sizeCache           protoimpl.SizeCache
+	// session this authorization request is associated with.
+	// This is a Pomerium implementation specific field.
+	SessionId     string `protobuf:"bytes,8,opt,name=session_id,json=sessionId,proto3" json:"session_id,omitempty"`
+	unknownFields protoimpl.UnknownFields
+	sizeCache     protoimpl.SizeCache
 }
 
 func (x *AuthorizationRequest) Reset() {
@@ -131,6 +134,13 @@ func (x *AuthorizationRequest) GetCodeChallengeMethod() string {
 	return ""
 }
 
+func (x *AuthorizationRequest) GetSessionId() string {
+	if x != nil {
+		return x.SessionId
+	}
+	return ""
+}
+
 var File_authorization_request_proto protoreflect.FileDescriptor
 
 var file_authorization_request_proto_rawDesc = string([]byte{
@@ -138,7 +148,7 @@ var file_authorization_request_proto_rawDesc = string([]byte{
 	0x72, 0x65, 0x71, 0x75, 0x65, 0x73, 0x74, 0x2e, 0x70, 0x72, 0x6f, 0x74, 0x6f, 0x12, 0x07, 0x6f,
 	0x61, 0x75, 0x74, 0x68, 0x32, 0x31, 0x1a, 0x1b, 0x62, 0x75, 0x66, 0x2f, 0x76, 0x61, 0x6c, 0x69,
 	0x64, 0x61, 0x74, 0x65, 0x2f, 0x76, 0x61, 0x6c, 0x69, 0x64, 0x61, 0x74, 0x65, 0x2e, 0x70, 0x72,
-	0x6f, 0x74, 0x6f, 0x22, 0x83, 0x03, 0x0a, 0x14, 0x41, 0x75, 0x74, 0x68, 0x6f, 0x72, 0x69, 0x7a,
+	0x6f, 0x74, 0x6f, 0x22, 0xaa, 0x03, 0x0a, 0x14, 0x41, 0x75, 0x74, 0x68, 0x6f, 0x72, 0x69, 0x7a,
 	0x61, 0x74, 0x69, 0x6f, 0x6e, 0x52, 0x65, 0x71, 0x75, 0x65, 0x73, 0x74, 0x12, 0x23, 0x0a, 0x09,
 	0x63, 0x6c, 0x69, 0x65, 0x6e, 0x74, 0x5f, 0x69, 0x64, 0x18, 0x01, 0x20, 0x01, 0x28, 0x09, 0x42,
 	0x06, 0xba, 0x48, 0x03, 0xc8, 0x01, 0x01, 0x52, 0x08, 0x63, 0x6c, 0x69, 0x65, 0x6e, 0x74, 0x49,
@@ -159,21 +169,24 @@ var file_authorization_request_proto_rawDesc = string([]byte{
 	0x18, 0x07, 0x20, 0x01, 0x28, 0x09, 0x42, 0x12, 0xba, 0x48, 0x0f, 0x72, 0x0d, 0x52, 0x04, 0x53,
 	0x32, 0x35, 0x36, 0x52, 0x05, 0x70, 0x6c, 0x61, 0x69, 0x6e, 0x48, 0x02, 0x52, 0x13, 0x63, 0x6f,
 	0x64, 0x65, 0x43, 0x68, 0x61, 0x6c, 0x6c, 0x65, 0x6e, 0x67, 0x65, 0x4d, 0x65, 0x74, 0x68, 0x6f,
-	0x64, 0x88, 0x01, 0x01, 0x42, 0x0f, 0x0a, 0x0d, 0x5f, 0x72, 0x65, 0x64, 0x69, 0x72, 0x65, 0x63,
-	0x74, 0x5f, 0x75, 0x72, 0x69, 0x42, 0x08, 0x0a, 0x06, 0x5f, 0x73, 0x74, 0x61, 0x74, 0x65, 0x42,
-	0x18, 0x0a, 0x16, 0x5f, 0x63, 0x6f, 0x64, 0x65, 0x5f, 0x63, 0x68, 0x61, 0x6c, 0x6c, 0x65, 0x6e,
-	0x67, 0x65, 0x5f, 0x6d, 0x65, 0x74, 0x68, 0x6f, 0x64, 0x42, 0xac, 0x01, 0x0a, 0x0b, 0x63, 0x6f,
-	0x6d, 0x2e, 0x6f, 0x61, 0x75, 0x74, 0x68, 0x32, 0x31, 0x42, 0x19, 0x41, 0x75, 0x74, 0x68, 0x6f,
-	0x72, 0x69, 0x7a, 0x61, 0x74, 0x69, 0x6f, 0x6e, 0x52, 0x65, 0x71, 0x75, 0x65, 0x73, 0x74, 0x50,
-	0x72, 0x6f, 0x74, 0x6f, 0x50, 0x01, 0x5a, 0x46, 0x67, 0x69, 0x74, 0x68, 0x75, 0x62, 0x2e, 0x63,
-	0x6f, 0x6d, 0x2f, 0x62, 0x75, 0x66, 0x62, 0x75, 0x69, 0x6c, 0x64, 0x2f, 0x62, 0x75, 0x66, 0x2d,
-	0x65, 0x78, 0x61, 0x6d, 0x70, 0x6c, 0x65, 0x73, 0x2f, 0x70, 0x72, 0x6f, 0x74, 0x6f, 0x76, 0x61,
-	0x6c, 0x69, 0x64, 0x61, 0x74, 0x65, 0x2f, 0x71, 0x75, 0x69, 0x63, 0x6b, 0x73, 0x74, 0x61, 0x72,
-	0x74, 0x2d, 0x67, 0x6f, 0x2f, 0x73, 0x74, 0x61, 0x72, 0x74, 0x2f, 0x67, 0x65, 0x6e, 0xa2, 0x02,
-	0x03, 0x4f, 0x58, 0x58, 0xaa, 0x02, 0x07, 0x4f, 0x61, 0x75, 0x74, 0x68, 0x32, 0x31, 0xca, 0x02,
-	0x07, 0x4f, 0x61, 0x75, 0x74, 0x68, 0x32, 0x31, 0xe2, 0x02, 0x13, 0x4f, 0x61, 0x75, 0x74, 0x68,
-	0x32, 0x31, 0x5c, 0x47, 0x50, 0x42, 0x4d, 0x65, 0x74, 0x61, 0x64, 0x61, 0x74, 0x61, 0xea, 0x02,
-	0x07, 0x4f, 0x61, 0x75, 0x74, 0x68, 0x32, 0x31, 0x62, 0x06, 0x70, 0x72, 0x6f, 0x74, 0x6f, 0x33,
+	0x64, 0x88, 0x01, 0x01, 0x12, 0x25, 0x0a, 0x0a, 0x73, 0x65, 0x73, 0x73, 0x69, 0x6f, 0x6e, 0x5f,
+	0x69, 0x64, 0x18, 0x08, 0x20, 0x01, 0x28, 0x09, 0x42, 0x06, 0xba, 0x48, 0x03, 0xc8, 0x01, 0x01,
+	0x52, 0x09, 0x73, 0x65, 0x73, 0x73, 0x69, 0x6f, 0x6e, 0x49, 0x64, 0x42, 0x0f, 0x0a, 0x0d, 0x5f,
+	0x72, 0x65, 0x64, 0x69, 0x72, 0x65, 0x63, 0x74, 0x5f, 0x75, 0x72, 0x69, 0x42, 0x08, 0x0a, 0x06,
+	0x5f, 0x73, 0x74, 0x61, 0x74, 0x65, 0x42, 0x18, 0x0a, 0x16, 0x5f, 0x63, 0x6f, 0x64, 0x65, 0x5f,
+	0x63, 0x68, 0x61, 0x6c, 0x6c, 0x65, 0x6e, 0x67, 0x65, 0x5f, 0x6d, 0x65, 0x74, 0x68, 0x6f, 0x64,
+	0x42, 0xac, 0x01, 0x0a, 0x0b, 0x63, 0x6f, 0x6d, 0x2e, 0x6f, 0x61, 0x75, 0x74, 0x68, 0x32, 0x31,
+	0x42, 0x19, 0x41, 0x75, 0x74, 0x68, 0x6f, 0x72, 0x69, 0x7a, 0x61, 0x74, 0x69, 0x6f, 0x6e, 0x52,
+	0x65, 0x71, 0x75, 0x65, 0x73, 0x74, 0x50, 0x72, 0x6f, 0x74, 0x6f, 0x50, 0x01, 0x5a, 0x46, 0x67,
+	0x69, 0x74, 0x68, 0x75, 0x62, 0x2e, 0x63, 0x6f, 0x6d, 0x2f, 0x62, 0x75, 0x66, 0x62, 0x75, 0x69,
+	0x6c, 0x64, 0x2f, 0x62, 0x75, 0x66, 0x2d, 0x65, 0x78, 0x61, 0x6d, 0x70, 0x6c, 0x65, 0x73, 0x2f,
+	0x70, 0x72, 0x6f, 0x74, 0x6f, 0x76, 0x61, 0x6c, 0x69, 0x64, 0x61, 0x74, 0x65, 0x2f, 0x71, 0x75,
+	0x69, 0x63, 0x6b, 0x73, 0x74, 0x61, 0x72, 0x74, 0x2d, 0x67, 0x6f, 0x2f, 0x73, 0x74, 0x61, 0x72,
+	0x74, 0x2f, 0x67, 0x65, 0x6e, 0xa2, 0x02, 0x03, 0x4f, 0x58, 0x58, 0xaa, 0x02, 0x07, 0x4f, 0x61,
+	0x75, 0x74, 0x68, 0x32, 0x31, 0xca, 0x02, 0x07, 0x4f, 0x61, 0x75, 0x74, 0x68, 0x32, 0x31, 0xe2,
+	0x02, 0x13, 0x4f, 0x61, 0x75, 0x74, 0x68, 0x32, 0x31, 0x5c, 0x47, 0x50, 0x42, 0x4d, 0x65, 0x74,
+	0x61, 0x64, 0x61, 0x74, 0x61, 0xea, 0x02, 0x07, 0x4f, 0x61, 0x75, 0x74, 0x68, 0x32, 0x31, 0x62,
+	0x06, 0x70, 0x72, 0x6f, 0x74, 0x6f, 0x33,
 })
 
 var (
diff --git a/internal/oauth21/proto/authorization_request.proto b/internal/oauth21/proto/authorization_request.proto
index 1402774ea..532167ce2 100644
--- a/internal/oauth21/proto/authorization_request.proto
+++ b/internal/oauth21/proto/authorization_request.proto
@@ -44,4 +44,8 @@ message AuthorizationRequest {
   // transformation method is S256 or plain.
   optional string code_challenge_method = 7
       [ (buf.validate.field).string = {in : [ "S256", "plain" ]} ];
+
+  // session this authorization request is associated with.
+  // This is a Pomerium implementation specific field.
+  string session_id = 8 [ (buf.validate.field).required = true ];
 }
diff --git a/internal/oauth21/validate_client_test.go b/internal/oauth21/validate_client_test.go
index 16e0e8010..8b70e359a 100644
--- a/internal/oauth21/validate_client_test.go
+++ b/internal/oauth21/validate_client_test.go
@@ -3,7 +3,7 @@ package oauth21_test
 import (
 	"testing"
 
-	"github.com/zeebo/assert"
+	"github.com/stretchr/testify/assert"
 	"google.golang.org/protobuf/proto"
 
 	"github.com/pomerium/pomerium/internal/oauth21"