fix(auth): verify BetterAuth sessions via cookie headers

apps/api/src/auth/auth.service.ts

@@ -21,6 +21,10 @@ interface VerifiedSession {
   session: Record<string, unknown>;
 }
 
+interface SessionHeaderCandidate {
+  headers: Record<string, string>;
+}
+
 @Injectable()
 export class AuthService {
   private readonly logger = new Logger(AuthService.name);
@@ -103,36 +107,27 @@ export class AuthService {
    * Only known-safe auth errors return null; everything else propagates as 500.
    */
   async verifySession(token: string): Promise<VerifiedSession | null> {
-    try {
-      // TODO(#411): BetterAuth getSession returns opaque types — replace when upstream exports typed interfaces
-      const session = await this.auth.api.getSession({
-        headers: {
-          authorization: `Bearer ${token}`,
-        },
-      });
+    let sawNonError = false;
 
-      if (!session) {
-        return null;
-      }
+    for (const candidate of this.buildSessionHeaderCandidates(token)) {
+      try {
+        // TODO(#411): BetterAuth getSession returns opaque types — replace when upstream exports typed interfaces
+        const session = await this.auth.api.getSession(candidate);
 
-      return {
-        user: session.user as Record<string, unknown>,
-        session: session.session as Record<string, unknown>,
-      };
-    } catch (error: unknown) {
-      // Only known-safe auth errors return null
-      if (error instanceof Error) {
-        const msg = error.message.toLowerCase();
-        const isExpectedAuthError =
-          msg.includes("invalid token") ||
-          msg.includes("token expired") ||
-          msg.includes("session expired") ||
-          msg.includes("session not found") ||
-          msg.includes("invalid session") ||
-          msg === "unauthorized" ||
-          msg === "expired";
+        if (!session) {
+          continue;
+        }
+
+        return {
+          user: session.user as Record<string, unknown>,
+          session: session.session as Record<string, unknown>,
+        };
+      } catch (error: unknown) {
+        if (error instanceof Error) {
+          if (this.isExpectedAuthError(error.message)) {
+            continue;
+          }
 
-        if (!isExpectedAuthError) {
           // Infrastructure or unexpected — propagate as 500
           const safeMessage = (error.stack ?? error.message).replace(
             /Bearer\s+\S+/gi,
@@ -141,14 +136,57 @@ export class AuthService {
           this.logger.error("Session verification failed due to unexpected error", safeMessage);
           throw error;
         }
+
+        // Non-Error thrown values — log once for observability, treat as auth failure
+        if (!sawNonError) {
+          const errorDetail = typeof error === "string" ? error : JSON.stringify(error);
+          this.logger.warn("Session verification received non-Error thrown value", errorDetail);
+          sawNonError = true;
+        }
       }
-      // Non-Error thrown values — log for observability, treat as auth failure
-      if (!(error instanceof Error)) {
-        const errorDetail = typeof error === "string" ? error : JSON.stringify(error);
-        this.logger.warn("Session verification received non-Error thrown value", errorDetail);
-      }
-      return null;
     }
+
+    return null;
+  }
+
+  private buildSessionHeaderCandidates(token: string): SessionHeaderCandidate[] {
+    const encodedToken = encodeURIComponent(token);
+
+    return [
+      {
+        headers: {
+          cookie: `__Secure-better-auth.session_token=${encodedToken}`,
+        },
+      },
+      {
+        headers: {
+          cookie: `better-auth.session_token=${encodedToken}`,
+        },
+      },
+      {
+        headers: {
+          cookie: `__Host-better-auth.session_token=${encodedToken}`,
+        },
+      },
+      {
+        headers: {
+          authorization: `Bearer ${token}`,
+        },
+      },
+    ];
+  }
+
+  private isExpectedAuthError(message: string): boolean {
+    const normalized = message.toLowerCase();
+    return (
+      normalized.includes("invalid token") ||
+      normalized.includes("token expired") ||
+      normalized.includes("session expired") ||
+      normalized.includes("session not found") ||
+      normalized.includes("invalid session") ||
+      normalized === "unauthorized" ||
+      normalized === "expired"
+    );
   }
 
   /**