Headers
- Dart course
- Advanced
- Lesson 34/83
- 5 min
Learn headers and authorization.
Headers
HTTP headers add metadata to requests and responses. Common headers: content-type (body type), authorization (token), accept (expected response type).
In Dart headers are a Map<String, String>: {'content-type': 'application/json', 'authorization': 'Bearer xyz'}.
Header keys are case-insensitive. Multiple values can be joined with commas.
The Bearer token pattern
In OAuth/JWT-based authentication, the authorization header takes the form Bearer <token>. Example: {'authorization': 'Bearer eyJhb...'}.
The token is usually obtained from a login endpoint and sent in this header on subsequent requests. The server validates the token and identifies the request.
Never put the token in the URL; it leaks in logs. Always use a header and store the token securely.
Practice Build a headers Map
Inside main add var headers = {'content-type': 'application/json', 'authorization': 'Bearer xyz123'};. Add print(headers.length);.
Starter code
void main() {
// build a Map with two headers; print its length
}Sample solution
void main() {
var headers = {
'content-type': 'application/json',
'authorization': 'Bearer xyz123',
};
print(headers.length);
}Expected output
2
Questions and answers
Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.
1 What does the Authorization header carry?
- Body
- Token/identity Correct answer
- URL
- Method
Explanation: the authorization header carries token/identity.
2 Match the headers
| Term | Meaning |
|---|---|
content-type |
Body type |
authorization |
Token |
accept |
Expected type |
cache-control |
Cache |
3 Bearer token header
var headers = {'authorization': '____ $token'};var headers = {'authorization': 'Bearer $token'};Explanation: 'Bearer $token' is the JWT/OAuth token pattern.