diff --git a/README.md b/README.md
index 072240b..aaf2a94 100644
--- a/README.md
+++ b/README.md
@@ -3,12 +3,13 @@
 AWS Lambda middleware that allows Yealink desk phones to unlock the front door and manage lockdown profiles via LenelS2 Elements.
 
 ```
-Yealink T54W/T58W → HTTPS GET → API Gateway → Lambda → LenelS2 Elements API
+Yealink T54W/T58W → HTTPS GET (?token=) → API Gateway (token authorizer) → Lambda → LenelS2 Elements API
 ```
 
 ## Architecture
 
 - **API Gateway (HTTP API)** — `GET /unlock`, `GET /lockdown`, `GET /lockdown/status` with throttling (5 burst / 2 sustained req/sec)
+- **Token authorizer Lambda** — a REQUEST-type Lambda authorizer validates the `?token=` query-string value (the same shared secret the phones already send) against the `/seahaven/door-unlock/auth-token` SSM parameter, so unauthenticated callers are rejected at the gateway (401/403) before any handler runs. Identity source is `$request.querystring.token`; results are cached 5 minutes. Fail-closed. The handlers also re-validate the token as defense-in-depth.
 - **Unlock Lambda** — validates a shared auth token, calls the Elements `TemporaryUnlock` command
 - **Lockdown Lambda** — toggles lockdown profiles (start/stop) and checks status, returns Yealink XML TextScreen responses
 - **Lockdown Poller Lambda** — VPC-connected, polls Elements API every 15 seconds for lockdown status (runs 4x per 1-minute EventBridge schedule)
@@ -46,15 +47,12 @@ Pressing the line key toggles the lockdown on/off and displays the current statu
 
 ## CI/CD
 
-Pushes to `main` trigger an AWS CodePipeline (V2) that runs `cdk deploy` via CodeBuild.
+GitHub Actions, using the Sea Haven reusable workflows:
 
-| Resource | Name |
-|----------|------|
-| Pipeline | `seahaven-door-unlock-api-pipeline` |
-| CodeBuild project | `seahaven-door-unlock-api-build` |
-| Artifact bucket | `seahaven-door-unlock-api-pipeline-artifacts` |
+- **`.github/workflows/ci.yaml`** — on pull requests to `main`, runs the `ci-typescript-cdk` reusable workflow (build, lint, synth).
+- **`.github/workflows/deploy.yaml`** — on push to `main`, runs the `cd-cdk` reusable workflow which assumes the `githubdeploy-seahaven-door-unlock-api` OIDC role (`AWS_DEPLOY_ROLE_ARN` repo secret) and runs `cdk deploy`.
 
-The CodeBuild role assumes CDK bootstrap roles for deployment — no separate CloudFormation stage.
+The legacy CodePipeline/CodeBuild deploy path has been fully decommissioned.
 
 ## Manual Deployment
 
diff --git a/buildspec.yml b/buildspec.yml
deleted file mode 100644
index cd2f3aa..0000000
--- a/buildspec.yml
+++ /dev/null
@@ -1,11 +0,0 @@
-version: 0.2
-
-phases:
-  install:
-    runtime-versions:
-      nodejs: 22
-    commands:
-      - npm ci
-  build:
-    commands:
-      - npx cdk deploy --require-approval never
diff --git a/lambda/authorizer/authorizer-handler.ts b/lambda/authorizer/authorizer-handler.ts
new file mode 100644
index 0000000..2e8f334
--- /dev/null
+++ b/lambda/authorizer/authorizer-handler.ts
@@ -0,0 +1,62 @@
+import {
+  SSMClient,
+  GetParameterCommand,
+} from "@aws-sdk/client-ssm";
+import { timingSafeEqual } from "node:crypto";
+
+const ssm = new SSMClient({});
+
+function tokensMatch(provided: string, expected: string): boolean {
+  const a = Buffer.from(provided);
+  const b = Buffer.from(expected);
+  // timingSafeEqual throws on unequal-length buffers; check length first.
+  return a.length === b.length && timingSafeEqual(a, b);
+}
+
+let cachedAuthToken: string | undefined;
+
+async function getAuthToken(): Promise<string> {
+  if (cachedAuthToken) return cachedAuthToken;
+  const res = await ssm.send(
+    new GetParameterCommand({
+      Name: process.env.AUTH_TOKEN_PARAM!,
+      WithDecryption: true,
+    })
+  );
+  cachedAuthToken = res.Parameter!.Value!;
+  return cachedAuthToken;
+}
+
+/**
+ * API Gateway HTTP API (payload v2.0) REQUEST Lambda authorizer.
+ *
+ * Validates the SAME `?token=` query-string parameter the Yealink XML Browser
+ * keys already send (type-17 keys issue a plain GET and cannot send headers or
+ * a POST body), so this authorizer is transparent to the phones. An
+ * unauthenticated or wrong-token request is now rejected at the gateway with
+ * 401/403 before any handler Lambda is invoked.
+ *
+ * Returns the simple-response shape ({ isAuthorized }) which the routes are
+ * configured for (enableSimpleResponses: true).
+ */
+export async function handler(event: {
+  queryStringParameters?: Record<string, string>;
+}): Promise<{ isAuthorized: boolean }> {
+  const token = event.queryStringParameters?.token;
+  if (!token) {
+    return { isAuthorized: false };
+  }
+
+  let expected: string;
+  try {
+    expected = await getAuthToken();
+  } catch (err) {
+    console.error(
+      JSON.stringify({ action: "authorize", status: "error", reason: "ssm_failure", error: String(err) })
+    );
+    // Fail closed: deny if the token cannot be loaded.
+    return { isAuthorized: false };
+  }
+
+  return { isAuthorized: tokensMatch(token, expected) };
+}
diff --git a/lib/door-unlock-stack.ts b/lib/door-unlock-stack.ts
index 6d20d1b..3278165 100644
--- a/lib/door-unlock-stack.ts
+++ b/lib/door-unlock-stack.ts
@@ -2,6 +2,7 @@ import * as cdk from "aws-cdk-lib";
 import * as lambda from "aws-cdk-lib/aws-lambda";
 import * as apigwv2 from "aws-cdk-lib/aws-apigatewayv2";
 import * as integrations from "aws-cdk-lib/aws-apigatewayv2-integrations";
+import * as authorizers from "aws-cdk-lib/aws-apigatewayv2-authorizers";
 import * as ssm from "aws-cdk-lib/aws-ssm";
 import * as secretsmanager from "aws-cdk-lib/aws-secretsmanager";
 import * as ec2 from "aws-cdk-lib/aws-ec2";
@@ -100,6 +101,57 @@ export class DoorUnlockStack extends cdk.Stack {
     elementsApiKeyParam.grantRead(lockdownHandler);
     authTokenParam.grantRead(lockdownHandler);
 
+    // Gateway authorizer (INFRA-99): validates the same `?token=` query-string
+    // value the Yealink XML Browser keys already send, so it is transparent to
+    // the phones while rejecting unauthenticated callers at the gateway.
+    const authorizerHandler = new lambda.Function(this, "AuthorizerHandler", {
+      functionName: "door-unlock-api-authorizer",
+      runtime: lambda.Runtime.NODEJS_22_X,
+      architecture: lambda.Architecture.ARM_64,
+      handler: "authorizer-handler.handler",
+      code: lambda.Code.fromAsset(path.join(__dirname, "../lambda/authorizer"), {
+        bundling: {
+          image: lambda.Runtime.NODEJS_22_X.bundlingImage,
+          local: {
+            tryBundle(outputDir: string) {
+              const { execSync } = require("child_process");
+              execSync(
+                `esbuild ${path.join(__dirname, "../lambda/authorizer/authorizer-handler.ts")} --bundle --platform=node --target=node22 --outfile=${path.join(outputDir, "authorizer-handler.js")} --external:@aws-sdk/*`
+              );
+              return true;
+            },
+          },
+        },
+      }),
+      environment: {
+        AUTH_TOKEN_PARAM: authTokenParam.parameterName,
+      },
+      // APIGW HTTP API authorizers have a hard 10s limit; keep margin so the
+      // gateway returns its own 500 rather than racing the Lambda timeout. The
+      // token is cached in module scope, so warm invocations never hit SSM.
+      timeout: cdk.Duration.seconds(8),
+      memorySize: 128,
+      logRetention: logs.RetentionDays.TWO_MONTHS,
+    });
+
+    authTokenParam.grantRead(authorizerHandler);
+
+    const tokenAuthorizer = new authorizers.HttpLambdaAuthorizer(
+      "DoorUnlockTokenAuthorizer",
+      authorizerHandler,
+      {
+        authorizerName: "door-unlock-api-token-authorizer",
+        // The Yealink phones send the token in the query string; scope the
+        // identity source there. A request with no `token` query param is
+        // rejected by the gateway before the authorizer Lambda is invoked.
+        identitySource: ["$request.querystring.token"],
+        responseTypes: [authorizers.HttpLambdaResponseType.SIMPLE],
+        // Authorizer result caching keyed on the identity source (the token).
+        // 5 min keeps repeated phone presses fast without a long stale window.
+        resultsCacheTtl: cdk.Duration.minutes(5),
+      }
+    );
+
     const vpc = ec2.Vpc.fromLookup(this, "SeaHavenVpc", {
       vpcId: "vpc-0d3d4b67bd0cf8a68",
     });
@@ -212,6 +264,7 @@ export class DoorUnlockStack extends cdk.Stack {
         "UnlockIntegration",
         unlockHandler
       ),
+      authorizer: tokenAuthorizer,
     });
 
     const lockdownIntegration = new integrations.HttpLambdaIntegration(
@@ -223,12 +276,14 @@ export class DoorUnlockStack extends cdk.Stack {
       path: "/lockdown",
       methods: [apigwv2.HttpMethod.GET],
       integration: lockdownIntegration,
+      authorizer: tokenAuthorizer,
     });
 
     httpApi.addRoutes({
       path: "/lockdown/status",
       methods: [apigwv2.HttpMethod.GET],
       integration: lockdownIntegration,
+      authorizer: tokenAuthorizer,
     });
 
     const hostedZone = route53.HostedZone.fromHostedZoneAttributes(