upstream: apply authentication through shared transport

Author: andrew

config.example.yaml

@@ -96,7 +96,8 @@ upstream:
   cargo_download: "https://static.crates.io/crates"
 
   # Authentication for upstream registries
-  # Keys are URL prefixes matched against request URLs.
+  # Keys are absolute URL scopes. Scheme, host, effective port, and path
+  # segment boundaries must match; the longest matching scope wins.
   # Values can reference environment variables using ${VAR_NAME} syntax.
   #
   # Supported auth types:

docs/architecture.md

@@ -240,6 +240,8 @@ Fetches artifacts from upstream registries.
 - Exponential backoff retry on 429 (rate limit) and 5xx errors
 - Returns streaming reader (doesn't load into memory)
 - Configurable user-agent
+- Shares an authentication-aware transport with metadata requests so URL-scoped credentials apply consistently
+- Discovers and caches scoped OCI Bearer tokens from registry challenges
 
 **Resolver:**
 - Determines download URL for a package/version

docs/configuration.md

@@ -123,7 +123,9 @@ upstream:
 
 ## Authentication
 
-Configure authentication for private upstream registries. Auth is matched by URL prefix, and credentials can reference environment variables using `${VAR_NAME}` syntax.
+Configure authentication for private upstream registries. The same authentication-aware client is used for metadata and artifact downloads, and credentials can reference environment variables using `${VAR_NAME}` syntax.
+
+OCI registries that return a Bearer challenge from a `/v2/{repository}/…` endpoint are handled automatically. The proxy discovers the token realm from `WWW-Authenticate`, applies any configured credentials for the token URL, and reuses the scoped token until shortly before it expires.
 
 ### Bearer Token
 
@@ -172,7 +174,7 @@ upstream:
 
 ### URL Matching
 
-Auth configs are matched by URL prefix. The longest matching prefix wins, so you can configure different credentials for different paths:
+Auth keys must be absolute URLs. Matching compares the scheme, host, effective port, and path-segment prefix, preventing credentials for `registry.example.com` from being sent to a lookalike host such as `registry.example.com.evil.test`. The longest matching scope wins, so you can configure different credentials for different paths:
 
 ```yaml
 upstream:

internal/config/config.go

@@ -274,23 +274,29 @@ type UpstreamConfig struct {
 	CargoDownload string `json:"cargo_download" yaml:"cargo_download"`
 
 	// Auth configures authentication for upstream registries.
-	// Keys are URL prefixes that are matched against request URLs.
+	// Keys are absolute URL scopes matched by scheme, host, effective port,
+	// and path-segment prefix.
 	// Example: "https://npm.pkg.github.com" matches all requests to that host.
 	Auth map[string]AuthConfig `json:"auth" yaml:"auth"`
 }
 
 // AuthForURL returns the auth config that matches the given URL.
-// Matches are based on URL prefix - the longest matching prefix wins.
+// The longest matching URL scope wins.
 func (u *UpstreamConfig) AuthForURL(url string) *AuthConfig {
 	if u.Auth == nil {
 		return nil
 	}
+	target, err := parseAuthURL(url)
+	if err != nil {
+		return nil
+	}
 
 	var bestMatch *AuthConfig
 	var bestLen int
 
 	for pattern, auth := range u.Auth {
-		if strings.HasPrefix(url, pattern) && len(pattern) > bestLen {
+		configured, err := parseAuthURL(pattern)
+		if err == nil && authURLMatches(configured, target) && len(pattern) > bestLen {
 			a := auth // copy to avoid loop variable capture
 			bestMatch = &a
 			bestLen = len(pattern)
@@ -300,6 +306,45 @@ func (u *UpstreamConfig) AuthForURL(url string) *AuthConfig {
 	return bestMatch
 }
 
+func parseAuthURL(value string) (*url.URL, error) {
+	parsed, err := url.Parse(value)
+	if err != nil || !parsed.IsAbs() || parsed.Hostname() == "" || parsed.Opaque != "" {
+		return nil, fmt.Errorf("invalid authentication URL")
+	}
+	return parsed, nil
+}
+
+func authURLMatches(configured, target *url.URL) bool {
+	if !strings.EqualFold(configured.Scheme, target.Scheme) ||
+		!strings.EqualFold(configured.Hostname(), target.Hostname()) ||
+		authURLPort(configured) != authURLPort(target) {
+		return false
+	}
+	if configured.RawQuery != "" && configured.RawQuery != target.RawQuery {
+		return false
+	}
+
+	configuredPath := strings.TrimSuffix(configured.EscapedPath(), "/")
+	if configuredPath == "" {
+		return true
+	}
+	targetPath := strings.TrimSuffix(target.EscapedPath(), "/")
+	return targetPath == configuredPath || strings.HasPrefix(targetPath, configuredPath+"/")
+}
+
+func authURLPort(value *url.URL) string {
+	if port := value.Port(); port != "" {
+		return port
+	}
+	if strings.EqualFold(value.Scheme, "https") {
+		return "443"
+	}
+	if strings.EqualFold(value.Scheme, "http") {
+		return "80"
+	}
+	return ""
+}
+
 // AuthConfig configures authentication for an upstream registry.
 type AuthConfig struct {
 	// Type is the authentication type: "bearer", "basic", or "header".

internal/config/config_test.go

@@ -760,3 +760,45 @@ func TestDatabaseConfigString(t *testing.T) {
 		}
 	}
 }
+
+func TestUpstreamAuthForURLMatchesURLComponents(t *testing.T) {
+	registryAuth := AuthConfig{Type: "bearer", Token: "registry-token"}
+	privateAuth := AuthConfig{Type: "bearer", Token: "private-token"}
+	config := UpstreamConfig{Auth: map[string]AuthConfig{
+		"https://registry.example.com":         registryAuth,
+		"https://registry.example.com/private": privateAuth,
+	}}
+
+	tests := []struct {
+		name      string
+		url       string
+		wantToken string
+	}{
+		{name: "registry root", url: "https://registry.example.com/package", wantToken: "registry-token"},
+		{name: "host is case insensitive", url: "https://REGISTRY.EXAMPLE.COM/package", wantToken: "registry-token"},
+		{name: "longest path match", url: "https://registry.example.com/private/package", wantToken: "private-token"},
+		{name: "exact path match", url: "https://registry.example.com/private", wantToken: "private-token"},
+		{name: "path segment boundary", url: "https://registry.example.com/private-other/package", wantToken: "registry-token"},
+		{name: "lookalike host rejected", url: "https://registry.example.com.evil.test/package"},
+		{name: "different scheme rejected", url: "http://registry.example.com/package"},
+		{name: "different port rejected", url: "https://registry.example.com:8443/package"},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			auth := config.AuthForURL(tt.url)
+			if tt.wantToken == "" {
+				if auth != nil {
+					t.Fatalf("AuthForURL() = %+v, want nil", auth)
+				}
+				return
+			}
+			if auth == nil {
+				t.Fatal("AuthForURL() = nil, want authentication")
+			}
+			if auth.Token != tt.wantToken {
+				t.Errorf("token = %q, want %q", auth.Token, tt.wantToken)
+			}
+		})
+	}
+}