API key authentication in Rest API - Step-by-Step Execution

Concept Flow - API key authentication

Client sends request with API key

↓

Server receives request

↓

Server checks if API key is present

↓

Server validates API key

↓

Is API key valid?

↓

Process request

↓

Send response to client

The client sends a request with an API key; the server checks if the key is present and valid before processing or rejecting the request.

Execution Sample

Rest API

GET /data HTTP/1.1
Host: api.example.com
API-Key: abc123

// Server checks API-Key header
// If valid, returns data
// Else returns error

A client sends a GET request with an API key; the server verifies the key and responds accordingly.

Execution Table

Step	Action	API Key Present?	API Key Valid?	Server Response
1	Receive request	Yes	Not checked yet	Waiting for validation
2	Check API key presence	Yes	Not checked yet	Proceed to validation
3	Validate API key	Yes	Yes	Process request and send data
4	Send response	Yes	Yes	200 OK with data
5	End	N/A	N/A	Request completed

💡 Request ends after sending response based on API key validity

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	Final
API Key Present	False	True	True	True	True
API Key Valid	False	False	False	True	True
Server Response	None	None	None	Data sent	Data sent

Key Moments - 3 Insights

What happens if the API key is missing in the request?

If the API key is missing, the server rejects the request immediately at Step 2, as shown in the flow where 'No' branch leads to rejection.

Why does the server check for API key presence before validating it?

The server first ensures the API key exists to avoid validating a missing key, which would cause errors. This is shown in Step 2 where presence is checked before validation.

What response does the server send if the API key is invalid?

If the API key is invalid, the server rejects the request with an error response instead of processing it, as indicated by the 'No' branch after validation in the flow.

Visual Quiz - 3 Questions

Look at the execution table, at which step does the server confirm the API key is valid?

A Step 2

B Step 3

C Step 4

D Step 1

💡 Hint

Check the 'API Key Valid?' column in the execution table to see when it changes to 'Yes'.

According to the variable tracker, what is the value of 'Server Response' after Step 3?

A None

B Error message

C Data sent

D Waiting

💡 Hint

Look at the 'Server Response' row in the variable tracker after Step 3.

If the API key was missing, how would the execution table change?

A API Key Present would be 'No' at Step 2 and server response would be rejection

B API Key Valid would be 'Yes' at Step 3

C Server would process the request anyway

D API Key Present would be 'Yes' at Step 1

💡 Hint

Refer to the concept flow where missing API key leads to immediate rejection.

Concept Snapshot

API key authentication requires clients to send a secret key with requests.
Server checks if the key is present and valid.
If valid, server processes the request.
If missing or invalid, server rejects with error.
This protects API access from unauthorized users.

Full Transcript

API key authentication works by the client sending a request with a special key called an API key. The server first checks if this key is included in the request. If the key is missing, the server rejects the request immediately. If the key is present, the server then checks if the key is valid. If the key is valid, the server processes the request and sends back the data. If the key is invalid, the server rejects the request with an error. This process ensures only authorized clients can use the API.