diff --git a/services/platform-service/src/lib/api-key-auth.ts b/services/platform-service/src/lib/api-key-auth.ts
index a5a3890c..fa47e7a9 100644
--- a/services/platform-service/src/lib/api-key-auth.ts
+++ b/services/platform-service/src/lib/api-key-auth.ts
@@ -59,6 +59,25 @@ function tokenCollection() {
   return getCollection<ApiTokenLookupDoc>('api_tokens', '/id');
 }
 
+function logApiKeyWarning(
+  req: FastifyRequest,
+  event: string,
+  details: Record<string, unknown> = {}
+): void {
+  req.log.warn(
+    {
+      event,
+      requestId: req.id,
+      productIdHeader: req.headers['x-product-id'],
+      apiKeyPrefix: req.apiKeyAuth?.prefix,
+      apiKeyTokenId: req.apiKeyAuth?.tokenId,
+      apiKeyProductId: req.apiKeyAuth?.productId,
+      ...details,
+    },
+    '[api-key] access rejected'
+  );
+}
+
 function extractApiKey(req: FastifyRequest): string | null {
   const header = req.headers['x-api-key'];
   if (typeof header === 'string' && header.trim().length > 0) {
@@ -163,12 +182,16 @@ function ensureApiKeyScopes(
 ): ApiKeyAuthPayload {
   const apiKey = req.apiKeyAuth;
   if (!apiKey) {
+    logApiKeyWarning(req, 'missing_api_key_context');
     throw new UnauthorizedError('API key required');
   }
 
   const productIdHeader = req.headers['x-product-id'];
   if (typeof productIdHeader === 'string' && productIdHeader.length > 0) {
     if (productIdHeader !== apiKey.productId) {
+      logApiKeyWarning(req, 'product_mismatch', {
+        requestedProductId: productIdHeader,
+      });
       throw new ForbiddenError('API key is not valid for the requested product');
     }
   }
@@ -177,11 +200,19 @@ function ensureApiKeyScopes(
     requiredScopes.length > 0 &&
     !requiredScopes.every(scope => tokenHasScope(apiKey.scopes, scope))
   ) {
+    logApiKeyWarning(req, 'missing_scope', {
+      requiredScopes,
+      grantedScopes: apiKey.scopes,
+    });
     throw new ForbiddenError('API key missing required scopes');
   }
 
   if (allowedTokenTypes && allowedTokenTypes.length > 0) {
     if (!allowedTokenTypes.includes(apiKey.tokenType)) {
+      logApiKeyWarning(req, 'token_type_not_permitted', {
+        allowedTokenTypes,
+        tokenType: apiKey.tokenType,
+      });
       throw new ForbiddenError('API key token type is not permitted for this route');
     }
   }
@@ -199,6 +230,10 @@ function enforceApiKeyRateLimit(req: FastifyRequest, rateLimitKey?: string): voi
   const compositeKey = `api-key:${req.apiKeyAuth.productId}:${req.apiKeyAuth.tokenId}:${rateLimitKey}`;
   const keyResult = rateLimitStore.checkAndRecord(compositeKey, keyRule);
   if (!keyResult.allowed) {
+    logApiKeyWarning(req, 'token_rate_limited', {
+      rateLimitKey,
+      retryAfterMs: keyResult.retryAfterMs,
+    });
     throw new TooManyRequestsError('API key rate limit exceeded', {
       retryAfter: Math.ceil((keyResult.retryAfterMs ?? 0) / 1000),
     });
@@ -210,6 +245,10 @@ function enforceApiKeyRateLimit(req: FastifyRequest, rateLimitKey?: string): voi
   const productCompositeKey = `api-key-product:${req.apiKeyAuth.productId}:${rateLimitKey}`;
   const productResult = rateLimitStore.checkAndRecord(productCompositeKey, productRule);
   if (!productResult.allowed) {
+    logApiKeyWarning(req, 'product_rate_limited', {
+      rateLimitKey,
+      retryAfterMs: productResult.retryAfterMs,
+    });
     throw new TooManyRequestsError('Product API key rate limit exceeded', {
       retryAfter: Math.ceil((productResult.retryAfterMs ?? 0) / 1000),
     });
@@ -264,15 +303,19 @@ export async function registerOptionalApiKeyContext(app: FastifyInstance): Promi
       limit: 10,
     });
 
+    let rejectionReason: string | null = null;
+
     for (const candidate of candidates) {
       const ok = await bcrypt.compare(rawKey, candidate.tokenHash);
       if (!ok) continue;
 
       if (candidate.tokenType === 'user_api') {
+        rejectionReason = 'user_api_not_allowed';
         continue;
       }
 
       if (candidate.environment !== getRuntimeEnvironment()) {
+        rejectionReason = 'environment_mismatch';
         continue;
       }
 
@@ -292,5 +335,15 @@ export async function registerOptionalApiKeyContext(app: FastifyInstance): Promi
         .catch(() => {});
       return;
     }
+
+    req.log.warn(
+      {
+        event: rejectionReason ?? 'invalid_api_key',
+        requestId: req.id,
+        apiKeyPrefix: prefix,
+        productIdHeader: req.headers['x-product-id'],
+      },
+      '[api-key] authentication failed'
+    );
   });
 }