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Allow ephemeral ports for loopback redirect URIs

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Native OAuth clients such as Claude Code publish loopback redirect URIs
without a port (http://localhost/callback) and pick an ephemeral port at
request time, as described in RFC 8252 section 7.3. The authorize flow
matched the requested redirect URI against the registered set with an
exact string comparison, so http://localhost:3118/callback was rejected
with invalid_redirect_uri even for a trusted, allow-listed client.

Make OAuth2Client.IsRedirectURIAllowed the single source of truth for
redirect matching: it keeps exact matching and adds loopback-aware
matching that ignores the port when scheme, host, path, and query agree.
The redundant document-level check and its duplicate loopback helper in
the CIMD resolver are removed, so both the registered-client and CIMD
paths now rely on one matcher.

Also add a pkg/netx package for the loopback helper.

Signed-off-by: Bryan Frimin <bryan@probo.com>
This commit is contained in:
Bryan Frimin
2026-06-30 18:27:39 +02:00
parent bbfd8a18b6
commit 5b92a7ba5a
7 changed files with 144 additions and 83 deletions
Download Patch File Download Diff File Expand all files Collapse all files

50
pkg/iam/oauth2/cimd.go
View File

@@ -33,7 +33,7 @@ import (
"go.probo.inc/probo/pkg/cachecontrol"
"go.probo.inc/probo/pkg/coredata"
"go.probo.inc/probo/pkg/gid"
"go.probo.inc/probo/pkg/net"
"go.probo.inc/probo/pkg/netx"
)
const (
@@ -239,7 +239,7 @@ func validateCIMDRedirectURI(redirectURI string) error {
switch parsed.Scheme {
case "https":
case "http":
if !net.IsLoopback(parsed.Hostname()) {
if !netx.IsLoopback(parsed.Hostname()) {
return NewError(
ErrInvalidClient,
WithDescription("client metadata document contains invalid redirect_uri"),
@@ -255,47 +255,6 @@ func validateCIMDRedirectURI(redirectURI string) error {
return nil
}
func cimdRedirectURIAllowed(doc *ClientMetadataDocument, redirectURI string) bool {
for _, allowed := range doc.RedirectURIs {
if redirectURI == allowed {
return true
}
if cimdLoopbackRedirectMatches(allowed, redirectURI) {
return true
}
}
return false
}
func cimdLoopbackRedirectMatches(registered, requested string) bool {
registeredURL, err := url.Parse(registered)
if err != nil {
return false
}
requestedURL, err := url.Parse(requested)
if err != nil {
return false
}
if registeredURL.Scheme != requestedURL.Scheme {
return false
}
if !net.IsLoopback(registeredURL.Hostname()) || !net.IsLoopback(requestedURL.Hostname()) {
return false
}
if registeredURL.Hostname() != requestedURL.Hostname() {
return false
}
return registeredURL.Path == requestedURL.Path &&
registeredURL.RawQuery == requestedURL.RawQuery
}
func (f *cimdFetcher) loadCache(clientIDURL string) (*ClientMetadataDocument, bool) {
raw, ok := f.cache.Load(clientIDURL)
if !ok {
@@ -338,7 +297,6 @@ func (s *Service) resolveClient(
ctx context.Context,
tx pg.Tx,
clientIDRaw string,
redirectURI string,
) (*coredata.OAuth2Client, error) {
if clientID, err := gid.ParseGID(clientIDRaw); err == nil {
if tx != nil {
@@ -373,10 +331,6 @@ func (s *Service) resolveClient(
return nil, err
}
if redirectURI != "" && !cimdRedirectURIAllowed(doc, redirectURI) {
return nil, ErrInvalidRedirectURI
}
client, err := s.upsertCIMDClient(ctx, tx, clientIDRaw, doc)
if err != nil {
return nil, err

24
pkg/iam/oauth2/cimd_test.go
View File

@@ -141,30 +141,6 @@ func TestValidateClientMetadataDocument(t *testing.T) {
)
}
func TestCIMDRedirectURIAllowed(t *testing.T) {
t.Parallel()
doc := &ClientMetadataDocument{
RedirectURIs: []string{
"https://chatgpt.com/connector/oauth/callback",
"http://127.0.0.1:53682/callback",
},
}
assert.True(
t,
cimdRedirectURIAllowed(doc, "https://chatgpt.com/connector/oauth/callback"),
)
assert.True(
t,
cimdRedirectURIAllowed(doc, "http://127.0.0.1:8080/callback"),
)
assert.False(
t,
cimdRedirectURIAllowed(doc, "https://evil.example/callback"),
)
}
func TestCIMDFetcherFetch(t *testing.T) {
t.Parallel()

10
pkg/iam/oauth2/service.go
View File

@@ -32,7 +32,7 @@ import (
"go.probo.inc/probo/pkg/crypto/rand"
"go.probo.inc/probo/pkg/gid"
"go.probo.inc/probo/pkg/iam/oauth2scope"
"go.probo.inc/probo/pkg/net"
"go.probo.inc/probo/pkg/netx"
"go.probo.inc/probo/pkg/page"
"go.probo.inc/probo/pkg/uri"
)
@@ -1060,7 +1060,7 @@ func (s *Service) RegisterClient(
}
case coredata.OAuth2ClientVisibilityPrivate:
if parsed.Scheme == "http" {
if !net.IsLoopback(parsed.Hostname()) {
if !netx.IsLoopback(parsed.Hostname()) {
return gid.Nil,
"",
NewError(
@@ -1433,13 +1433,11 @@ func (s *Service) Authorize(
if err := s.pg.WithTx(
ctx,
func(ctx context.Context, tx pg.Tx) error {
client, err := s.resolveClient(ctx, tx, req.ClientIDRaw, req.RedirectURI)
client, err := s.resolveClient(ctx, tx, req.ClientIDRaw)
if err != nil {
return err
}
fmt.Printf("X: %+v\n", client)
if !client.IsRedirectURIAllowed(req.RedirectURI) {
return ErrInvalidRedirectURI
}
@@ -1738,7 +1736,7 @@ func (s *Service) AuthenticateClient(
clientIDRaw string,
clientSecret string,
) (*coredata.OAuth2Client, error) {
client, err := s.resolveClient(ctx, nil, clientIDRaw, "")
client, err := s.resolveClient(ctx, nil, clientIDRaw)
if err != nil {
return nil, err
}