feat(amp): add per-client upstream API key mapping support

internal/api/modules/amp/amp.go

@@ -227,11 +227,20 @@ func (m *AmpModule) OnConfigUpdated(cfg *config.Config) error {
 			}
 		}
 
-		// Check API key change
+		// Check API key change (both default and per-client mappings)
 		apiKeyChanged := m.hasAPIKeyChanged(oldSettings, &newSettings)
-		if apiKeyChanged {
+		upstreamAPIKeysChanged := m.hasUpstreamAPIKeysChanged(oldSettings, &newSettings)
+		if apiKeyChanged || upstreamAPIKeysChanged {
 			if m.secretSource != nil {
-				if ms, ok := m.secretSource.(*MultiSourceSecret); ok {
+				if ms, ok := m.secretSource.(*MappedSecretSource); ok {
+					if apiKeyChanged {
+						ms.UpdateDefaultExplicitKey(newSettings.UpstreamAPIKey)
+						ms.InvalidateCache()
+					}
+					if upstreamAPIKeysChanged {
+						ms.UpdateMappings(newSettings.UpstreamAPIKeys)
+					}
+				} else if ms, ok := m.secretSource.(*MultiSourceSecret); ok {
 					ms.UpdateExplicitKey(newSettings.UpstreamAPIKey)
 					ms.InvalidateCache()
 				}
@@ -251,10 +260,22 @@ func (m *AmpModule) OnConfigUpdated(cfg *config.Config) error {
 
 func (m *AmpModule) enableUpstreamProxy(upstreamURL string, settings *config.AmpCode) error {
 	if m.secretSource == nil {
-		m.secretSource = NewMultiSourceSecret(settings.UpstreamAPIKey, 0 /* default 5min */)
+		// Create MultiSourceSecret as the default source, then wrap with MappedSecretSource
+		defaultSource := NewMultiSourceSecret(settings.UpstreamAPIKey, 0 /* default 5min */)
+		mappedSource := NewMappedSecretSource(defaultSource)
+		mappedSource.UpdateMappings(settings.UpstreamAPIKeys)
+		m.secretSource = mappedSource
+	} else if ms, ok := m.secretSource.(*MappedSecretSource); ok {
+		ms.UpdateDefaultExplicitKey(settings.UpstreamAPIKey)
+		ms.InvalidateCache()
+		ms.UpdateMappings(settings.UpstreamAPIKeys)
 	} else if ms, ok := m.secretSource.(*MultiSourceSecret); ok {
+		// Legacy path: wrap existing MultiSourceSecret with MappedSecretSource
 		ms.UpdateExplicitKey(settings.UpstreamAPIKey)
 		ms.InvalidateCache()
+		mappedSource := NewMappedSecretSource(ms)
+		mappedSource.UpdateMappings(settings.UpstreamAPIKeys)
+		m.secretSource = mappedSource
 	}
 
 	proxy, err := createReverseProxy(upstreamURL, m.secretSource)
@@ -313,6 +334,66 @@ func (m *AmpModule) hasAPIKeyChanged(old *config.AmpCode, new *config.AmpCode) b
 	return oldKey != newKey
 }
 
+// hasUpstreamAPIKeysChanged compares old and new per-client upstream API key mappings.
+func (m *AmpModule) hasUpstreamAPIKeysChanged(old *config.AmpCode, new *config.AmpCode) bool {
+	if old == nil {
+		return len(new.UpstreamAPIKeys) > 0
+	}
+
+	if len(old.UpstreamAPIKeys) != len(new.UpstreamAPIKeys) {
+		return true
+	}
+
+	// Build map for comparison: upstreamKey -> set of clientKeys
+	type entryInfo struct {
+		upstreamKey string
+		clientKeys  map[string]struct{}
+	}
+	oldEntries := make([]entryInfo, len(old.UpstreamAPIKeys))
+	for i, entry := range old.UpstreamAPIKeys {
+		clientKeys := make(map[string]struct{}, len(entry.APIKeys))
+		for _, k := range entry.APIKeys {
+			trimmed := strings.TrimSpace(k)
+			if trimmed == "" {
+				continue
+			}
+			clientKeys[trimmed] = struct{}{}
+		}
+		oldEntries[i] = entryInfo{
+			upstreamKey: strings.TrimSpace(entry.UpstreamAPIKey),
+			clientKeys:  clientKeys,
+		}
+	}
+
+	for i, newEntry := range new.UpstreamAPIKeys {
+		if i >= len(oldEntries) {
+			return true
+		}
+		oldE := oldEntries[i]
+		if strings.TrimSpace(newEntry.UpstreamAPIKey) != oldE.upstreamKey {
+			return true
+		}
+		newKeys := make(map[string]struct{}, len(newEntry.APIKeys))
+		for _, k := range newEntry.APIKeys {
+			trimmed := strings.TrimSpace(k)
+			if trimmed == "" {
+				continue
+			}
+			newKeys[trimmed] = struct{}{}
+		}
+		if len(newKeys) != len(oldE.clientKeys) {
+			return true
+		}
+		for k := range newKeys {
+			if _, ok := oldE.clientKeys[k]; !ok {
+				return true
+			}
+		}
+	}
+
+	return false
+}
+
 // GetModelMapper returns the model mapper instance (for testing/debugging).
 func (m *AmpModule) GetModelMapper() *DefaultModelMapper {
 	return m.modelMapper

internal/api/modules/amp/amp_test.go

@@ -312,3 +312,41 @@ func TestAmpModule_ProviderAliasesAlwaysRegistered(t *testing.T) {
 		})
 	}
 }
+
+func TestAmpModule_hasUpstreamAPIKeysChanged_DetectsRemovedKeyWithDuplicateInput(t *testing.T) {
+	m := &AmpModule{}
+
+	oldCfg := &config.AmpCode{
+		UpstreamAPIKeys: []config.AmpUpstreamAPIKeyEntry{
+			{UpstreamAPIKey: "u1", APIKeys: []string{"k1", "k2"}},
+		},
+	}
+	newCfg := &config.AmpCode{
+		UpstreamAPIKeys: []config.AmpUpstreamAPIKeyEntry{
+			{UpstreamAPIKey: "u1", APIKeys: []string{"k1", "k1"}},
+		},
+	}
+
+	if !m.hasUpstreamAPIKeysChanged(oldCfg, newCfg) {
+		t.Fatal("expected change to be detected when k2 is removed but new list contains duplicates")
+	}
+}
+
+func TestAmpModule_hasUpstreamAPIKeysChanged_IgnoresEmptyAndWhitespaceKeys(t *testing.T) {
+	m := &AmpModule{}
+
+	oldCfg := &config.AmpCode{
+		UpstreamAPIKeys: []config.AmpUpstreamAPIKeyEntry{
+			{UpstreamAPIKey: "u1", APIKeys: []string{"k1", "k2"}},
+		},
+	}
+	newCfg := &config.AmpCode{
+		UpstreamAPIKeys: []config.AmpUpstreamAPIKeyEntry{
+			{UpstreamAPIKey: "u1", APIKeys: []string{"  k1  ", "", "k2", "   "}},
+		},
+	}
+
+	if m.hasUpstreamAPIKeysChanged(oldCfg, newCfg) {
+		t.Fatal("expected no change when only whitespace/empty entries differ")
+	}
+}

internal/api/modules/amp/proxy.go

@@ -15,6 +15,33 @@ import (
 	log "github.com/sirupsen/logrus"
 )
 
+func removeQueryValuesMatching(req *http.Request, key string, match string) {
+	if req == nil || req.URL == nil || match == "" {
+		return
+	}
+
+	q := req.URL.Query()
+	values, ok := q[key]
+	if !ok || len(values) == 0 {
+		return
+	}
+
+	kept := make([]string, 0, len(values))
+	for _, v := range values {
+		if v == match {
+			continue
+		}
+		kept = append(kept, v)
+	}
+
+	if len(kept) == 0 {
+		q.Del(key)
+	} else {
+		q[key] = kept
+	}
+	req.URL.RawQuery = q.Encode()
+}
+
 // readCloser wraps a reader and forwards Close to a separate closer.
 // Used to restore peeked bytes while preserving upstream body Close behavior.
 type readCloser struct {
@@ -45,6 +72,14 @@ func createReverseProxy(upstreamURL string, secretSource SecretSource) (*httputi
 		// We will set our own Authorization using the configured upstream-api-key
 		req.Header.Del("Authorization")
 		req.Header.Del("X-Api-Key")
+		req.Header.Del("X-Goog-Api-Key")
+
+		// Remove query-based credentials if they match the authenticated client API key.
+		// This prevents leaking client auth material to the Amp upstream while avoiding
+		// breaking unrelated upstream query parameters.
+		clientKey := getClientAPIKeyFromContext(req.Context())
+		removeQueryValuesMatching(req, "key", clientKey)
+		removeQueryValuesMatching(req, "auth_token", clientKey)
 
 		// Preserve correlation headers for debugging
 		if req.Header.Get("X-Request-ID") == "" {

internal/api/modules/amp/proxy_test.go

@@ -3,11 +3,15 @@ package amp
 import (
 	"bytes"
 	"compress/gzip"
+	"context"
 	"fmt"
 	"io"
 	"net/http"
 	"net/http/httptest"
+	"strings"
 	"testing"
+
+	"github.com/router-for-me/CLIProxyAPI/v6/internal/config"
 )
 
 // Helper: compress data with gzip
@@ -306,6 +310,159 @@ func TestReverseProxy_EmptySecret(t *testing.T) {
 	}
 }
 
+func TestReverseProxy_StripsClientCredentialsFromHeadersAndQuery(t *testing.T) {
+	type captured struct {
+		headers http.Header
+		query   string
+	}
+	got := make(chan captured, 1)
+	upstream := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		got <- captured{headers: r.Header.Clone(), query: r.URL.RawQuery}
+		w.WriteHeader(200)
+		w.Write([]byte(`ok`))
+	}))
+	defer upstream.Close()
+
+	proxy, err := createReverseProxy(upstream.URL, NewStaticSecretSource("upstream"))
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		// Simulate clientAPIKeyMiddleware injection (per-request)
+		ctx := context.WithValue(r.Context(), clientAPIKeyContextKey{}, "client-key")
+		proxy.ServeHTTP(w, r.WithContext(ctx))
+	}))
+	defer srv.Close()
+
+	req, err := http.NewRequest(http.MethodGet, srv.URL+"/test?key=client-key&key=keep&auth_token=client-key&foo=bar", nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	req.Header.Set("Authorization", "Bearer client-key")
+	req.Header.Set("X-Api-Key", "client-key")
+	req.Header.Set("X-Goog-Api-Key", "client-key")
+
+	res, err := http.DefaultClient.Do(req)
+	if err != nil {
+		t.Fatal(err)
+	}
+	res.Body.Close()
+
+	c := <-got
+
+	// These are client-provided credentials and must not reach the upstream.
+	if v := c.headers.Get("X-Goog-Api-Key"); v != "" {
+		t.Fatalf("X-Goog-Api-Key should be stripped, got: %q", v)
+	}
+
+	// We inject upstream Authorization/X-Api-Key, so the client auth must not survive.
+	if v := c.headers.Get("Authorization"); v != "Bearer upstream" {
+		t.Fatalf("Authorization should be upstream-injected, got: %q", v)
+	}
+	if v := c.headers.Get("X-Api-Key"); v != "upstream" {
+		t.Fatalf("X-Api-Key should be upstream-injected, got: %q", v)
+	}
+
+	// Query-based credentials should be stripped only when they match the authenticated client key.
+	// Should keep unrelated values and parameters.
+	if strings.Contains(c.query, "auth_token=client-key") || strings.Contains(c.query, "key=client-key") {
+		t.Fatalf("query credentials should be stripped, got raw query: %q", c.query)
+	}
+	if !strings.Contains(c.query, "key=keep") || !strings.Contains(c.query, "foo=bar") {
+		t.Fatalf("expected query to keep non-credential params, got raw query: %q", c.query)
+	}
+}
+
+func TestReverseProxy_InjectsMappedSecret_FromRequestContext(t *testing.T) {
+	gotHeaders := make(chan http.Header, 1)
+	upstream := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		gotHeaders <- r.Header.Clone()
+		w.WriteHeader(200)
+		w.Write([]byte(`ok`))
+	}))
+	defer upstream.Close()
+
+	defaultSource := NewStaticSecretSource("default")
+	mapped := NewMappedSecretSource(defaultSource)
+	mapped.UpdateMappings([]config.AmpUpstreamAPIKeyEntry{
+		{
+			UpstreamAPIKey: "u1",
+			APIKeys:        []string{"k1"},
+		},
+	})
+
+	proxy, err := createReverseProxy(upstream.URL, mapped)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		// Simulate clientAPIKeyMiddleware injection (per-request)
+		ctx := context.WithValue(r.Context(), clientAPIKeyContextKey{}, "k1")
+		proxy.ServeHTTP(w, r.WithContext(ctx))
+	}))
+	defer srv.Close()
+
+	res, err := http.Get(srv.URL + "/test")
+	if err != nil {
+		t.Fatal(err)
+	}
+	res.Body.Close()
+
+	hdr := <-gotHeaders
+	if hdr.Get("X-Api-Key") != "u1" {
+		t.Fatalf("X-Api-Key missing or wrong, got: %q", hdr.Get("X-Api-Key"))
+	}
+	if hdr.Get("Authorization") != "Bearer u1" {
+		t.Fatalf("Authorization missing or wrong, got: %q", hdr.Get("Authorization"))
+	}
+}
+
+func TestReverseProxy_MappedSecret_FallsBackToDefault(t *testing.T) {
+	gotHeaders := make(chan http.Header, 1)
+	upstream := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		gotHeaders <- r.Header.Clone()
+		w.WriteHeader(200)
+		w.Write([]byte(`ok`))
+	}))
+	defer upstream.Close()
+
+	defaultSource := NewStaticSecretSource("default")
+	mapped := NewMappedSecretSource(defaultSource)
+	mapped.UpdateMappings([]config.AmpUpstreamAPIKeyEntry{
+		{
+			UpstreamAPIKey: "u1",
+			APIKeys:        []string{"k1"},
+		},
+	})
+
+	proxy, err := createReverseProxy(upstream.URL, mapped)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		ctx := context.WithValue(r.Context(), clientAPIKeyContextKey{}, "k2")
+		proxy.ServeHTTP(w, r.WithContext(ctx))
+	}))
+	defer srv.Close()
+
+	res, err := http.Get(srv.URL + "/test")
+	if err != nil {
+		t.Fatal(err)
+	}
+	res.Body.Close()
+
+	hdr := <-gotHeaders
+	if hdr.Get("X-Api-Key") != "default" {
+		t.Fatalf("X-Api-Key fallback missing or wrong, got: %q", hdr.Get("X-Api-Key"))
+	}
+	if hdr.Get("Authorization") != "Bearer default" {
+		t.Fatalf("Authorization fallback missing or wrong, got: %q", hdr.Get("Authorization"))
+	}
+}
+
 func TestReverseProxy_ErrorHandler(t *testing.T) {
 	// Point proxy to a non-routable address to trigger error
 	proxy, err := createReverseProxy("http://127.0.0.1:1", NewStaticSecretSource(""))

internal/api/modules/amp/routes.go

@@ -1,6 +1,7 @@
 package amp
 
 import (
+	"context"
 	"errors"
 	"net"
 	"net/http"
@@ -16,6 +17,37 @@ import (
 	log "github.com/sirupsen/logrus"
 )
 
+// clientAPIKeyContextKey is the context key used to pass the client API key
+// from gin.Context to the request context for SecretSource lookup.
+type clientAPIKeyContextKey struct{}
+
+// clientAPIKeyMiddleware injects the authenticated client API key from gin.Context["apiKey"]
+// into the request context so that SecretSource can look it up for per-client upstream routing.
+func clientAPIKeyMiddleware() gin.HandlerFunc {
+	return func(c *gin.Context) {
+		// Extract the client API key from gin context (set by AuthMiddleware)
+		if apiKey, exists := c.Get("apiKey"); exists {
+			if keyStr, ok := apiKey.(string); ok && keyStr != "" {
+				// Inject into request context for SecretSource.Get(ctx) to read
+				ctx := context.WithValue(c.Request.Context(), clientAPIKeyContextKey{}, keyStr)
+				c.Request = c.Request.WithContext(ctx)
+			}
+		}
+		c.Next()
+	}
+}
+
+// getClientAPIKeyFromContext retrieves the client API key from request context.
+// Returns empty string if not present.
+func getClientAPIKeyFromContext(ctx context.Context) string {
+	if val := ctx.Value(clientAPIKeyContextKey{}); val != nil {
+		if keyStr, ok := val.(string); ok {
+			return keyStr
+		}
+	}
+	return ""
+}
+
 // localhostOnlyMiddleware returns a middleware that dynamically checks the module's
 // localhost restriction setting. This allows hot-reload of the restriction without restarting.
 func (m *AmpModule) localhostOnlyMiddleware() gin.HandlerFunc {
@@ -129,6 +161,9 @@ func (m *AmpModule) registerManagementRoutes(engine *gin.Engine, baseHandler *ha
 		authWithBypass = wrapManagementAuth(auth, "/threads", "/auth", "/docs", "/settings")
 	}
 
+	// Inject client API key into request context for per-client upstream routing
+	ampAPI.Use(clientAPIKeyMiddleware())
+
 	// Dynamic proxy handler that uses m.getProxy() for hot-reload support
 	proxyHandler := func(c *gin.Context) {
 		// Swallow ErrAbortHandler panics from ReverseProxy copyResponse to avoid noisy stack traces
@@ -175,6 +210,8 @@ func (m *AmpModule) registerManagementRoutes(engine *gin.Engine, baseHandler *ha
 	if authWithBypass != nil {
 		rootMiddleware = append(rootMiddleware, authWithBypass)
 	}
+	// Add clientAPIKeyMiddleware after auth for per-client upstream routing
+	rootMiddleware = append(rootMiddleware, clientAPIKeyMiddleware())
 	engine.GET("/threads", append(rootMiddleware, proxyHandler)...)
 	engine.GET("/threads/*path", append(rootMiddleware, proxyHandler)...)
 	engine.GET("/docs", append(rootMiddleware, proxyHandler)...)
@@ -244,6 +281,8 @@ func (m *AmpModule) registerProviderAliases(engine *gin.Engine, baseHandler *han
 	if auth != nil {
 		ampProviders.Use(auth)
 	}
+	// Inject client API key into request context for per-client upstream routing
+	ampProviders.Use(clientAPIKeyMiddleware())
 
 	provider := ampProviders.Group("/:provider")
 

internal/api/modules/amp/secret.go

@@ -9,6 +9,9 @@ import (
 	"strings"
 	"sync"
 	"time"
+
+	"github.com/router-for-me/CLIProxyAPI/v6/internal/config"
+	log "github.com/sirupsen/logrus"
 )
 
 // SecretSource provides Amp API keys with configurable precedence and caching
@@ -164,3 +167,82 @@ func NewStaticSecretSource(key string) *StaticSecretSource {
 func (s *StaticSecretSource) Get(ctx context.Context) (string, error) {
 	return s.key, nil
 }
+
+// MappedSecretSource wraps a default SecretSource and adds per-client API key mapping.
+// When a request context contains a client API key that matches a configured mapping,
+// the corresponding upstream key is returned. Otherwise, falls back to the default source.
+type MappedSecretSource struct {
+	defaultSource SecretSource
+	mu            sync.RWMutex
+	lookup        map[string]string // clientKey -> upstreamKey
+}
+
+// NewMappedSecretSource creates a MappedSecretSource wrapping the given default source.
+func NewMappedSecretSource(defaultSource SecretSource) *MappedSecretSource {
+	return &MappedSecretSource{
+		defaultSource: defaultSource,
+		lookup:        make(map[string]string),
+	}
+}
+
+// Get retrieves the Amp API key, checking per-client mappings first.
+// If the request context contains a client API key that matches a configured mapping,
+// returns the corresponding upstream key. Otherwise, falls back to the default source.
+func (s *MappedSecretSource) Get(ctx context.Context) (string, error) {
+	// Try to get client API key from request context
+	clientKey := getClientAPIKeyFromContext(ctx)
+	if clientKey != "" {
+		s.mu.RLock()
+		if upstreamKey, ok := s.lookup[clientKey]; ok && upstreamKey != "" {
+			s.mu.RUnlock()
+			return upstreamKey, nil
+		}
+		s.mu.RUnlock()
+	}
+
+	// Fall back to default source
+	return s.defaultSource.Get(ctx)
+}
+
+// UpdateMappings rebuilds the client-to-upstream key mapping from configuration entries.
+// If the same client key appears in multiple entries, logs a warning and uses the first one.
+func (s *MappedSecretSource) UpdateMappings(entries []config.AmpUpstreamAPIKeyEntry) {
+	newLookup := make(map[string]string)
+
+	for _, entry := range entries {
+		upstreamKey := strings.TrimSpace(entry.UpstreamAPIKey)
+		if upstreamKey == "" {
+			continue
+		}
+		for _, clientKey := range entry.APIKeys {
+			trimmedKey := strings.TrimSpace(clientKey)
+			if trimmedKey == "" {
+				continue
+			}
+			if _, exists := newLookup[trimmedKey]; exists {
+				// Log warning for duplicate client key, first one wins
+				log.Warnf("amp upstream-api-keys: client API key appears in multiple entries; using first mapping.")
+				continue
+			}
+			newLookup[trimmedKey] = upstreamKey
+		}
+	}
+
+	s.mu.Lock()
+	s.lookup = newLookup
+	s.mu.Unlock()
+}
+
+// UpdateDefaultExplicitKey updates the explicit key on the underlying MultiSourceSecret (if applicable).
+func (s *MappedSecretSource) UpdateDefaultExplicitKey(key string) {
+	if ms, ok := s.defaultSource.(*MultiSourceSecret); ok {
+		ms.UpdateExplicitKey(key)
+	}
+}
+
+// InvalidateCache invalidates cache on the underlying MultiSourceSecret (if applicable).
+func (s *MappedSecretSource) InvalidateCache() {
+	if ms, ok := s.defaultSource.(*MultiSourceSecret); ok {
+		ms.InvalidateCache()
+	}
+}

internal/api/modules/amp/secret_test.go

@@ -8,6 +8,10 @@ import (
 	"sync"
 	"testing"
 	"time"
+
+	"github.com/router-for-me/CLIProxyAPI/v6/internal/config"
+	log "github.com/sirupsen/logrus"
+	"github.com/sirupsen/logrus/hooks/test"
 )
 
 func TestMultiSourceSecret_PrecedenceOrder(t *testing.T) {
@@ -278,3 +282,85 @@ func TestMultiSourceSecret_CacheEmptyResult(t *testing.T) {
 		t.Fatalf("after cache expiry, expected new-value, got %q", got3)
 	}
 }
+
+func TestMappedSecretSource_UsesMappingFromContext(t *testing.T) {
+	defaultSource := NewStaticSecretSource("default")
+	s := NewMappedSecretSource(defaultSource)
+	s.UpdateMappings([]config.AmpUpstreamAPIKeyEntry{
+		{
+			UpstreamAPIKey: "u1",
+			APIKeys:        []string{"k1"},
+		},
+	})
+
+	ctx := context.WithValue(context.Background(), clientAPIKeyContextKey{}, "k1")
+	got, err := s.Get(ctx)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if got != "u1" {
+		t.Fatalf("want u1, got %q", got)
+	}
+
+	ctx = context.WithValue(context.Background(), clientAPIKeyContextKey{}, "k2")
+	got, err = s.Get(ctx)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if got != "default" {
+		t.Fatalf("want default fallback, got %q", got)
+	}
+}
+
+func TestMappedSecretSource_DuplicateClientKey_FirstWins(t *testing.T) {
+	defaultSource := NewStaticSecretSource("default")
+	s := NewMappedSecretSource(defaultSource)
+	s.UpdateMappings([]config.AmpUpstreamAPIKeyEntry{
+		{
+			UpstreamAPIKey: "u1",
+			APIKeys:        []string{"k1"},
+		},
+		{
+			UpstreamAPIKey: "u2",
+			APIKeys:        []string{"k1"},
+		},
+	})
+
+	ctx := context.WithValue(context.Background(), clientAPIKeyContextKey{}, "k1")
+	got, err := s.Get(ctx)
+	if err != nil {
+		t.Fatalf("unexpected error: %v", err)
+	}
+	if got != "u1" {
+		t.Fatalf("want u1 (first wins), got %q", got)
+	}
+}
+
+func TestMappedSecretSource_DuplicateClientKey_LogsWarning(t *testing.T) {
+	hook := test.NewLocal(log.StandardLogger())
+	defer hook.Reset()
+
+	defaultSource := NewStaticSecretSource("default")
+	s := NewMappedSecretSource(defaultSource)
+	s.UpdateMappings([]config.AmpUpstreamAPIKeyEntry{
+		{
+			UpstreamAPIKey: "u1",
+			APIKeys:        []string{"k1"},
+		},
+		{
+			UpstreamAPIKey: "u2",
+			APIKeys:        []string{"k1"},
+		},
+	})
+
+	foundWarning := false
+	for _, entry := range hook.AllEntries() {
+		if entry.Level == log.WarnLevel && entry.Message == "amp upstream-api-keys: client API key appears in multiple entries; using first mapping." {
+			foundWarning = true
+			break
+		}
+	}
+	if !foundWarning {
+		t.Fatal("expected warning log for duplicate client key, but none was found")
+	}
+}