Understanding app_id, app_key, and app_secret: Securing Third‑Party API Calls

app_id Parameter

In most cases, app_id identifies a user or merchant account, similar to a customer_no in payment systems, linking the account to a specific entity. The platform uses this identifier to recognize who you are, but it is rarely sent alone; it is usually combined with a secret key for authentication.

app_key and app_secret

When a single app_id cannot express different permission levels—such as read‑only versus read‑write for the same business—additional credentials are needed. app_key and app_secret are introduced to allocate permissions at a finer granularity. For example, in an OSS storage service, one pair of app_key/app_secret might grant delete rights for backend management, while another pair provides only read/write rights for client‑side operations.

Typically, app_key and app_secret are used during the initial authentication request. After successful verification, the platform returns a token (often with an expiration time) that is used for subsequent interactions.

The app_key identifies which permissions the caller is requesting, while the app_secret proves that the caller actually possesses those permissions. When there is only one user and a single permission set, app_key and app_id become effectively equivalent.

Different Usage Patterns

Pattern 1: Open APIs (e.g., map services) may omit app_id and app_key, treating them as the same value used solely for usage statistics.

Pattern 2: Some services (e.g., Qiniu Cloud) provide only app_key and app_secret. The client generates a token locally using a specific algorithm, and the token is sent with each request.

Pattern 3: The client sends both app_key and app_secret to the server, which returns a token for subsequent API calls.

Pattern 4: For higher security, each request is signed (e.g., using MD5 or SHA1). The request parameters are sorted by key, concatenated as key=value&key=value, the app_secret string is appended, and a signature is computed. The signature (and all other parameters except app_secret) is sent to the server, which verifies the signature to ensure the message was not tampered with. Tencent Cloud adopts this approach.