Headers

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.

Exercise Build a headers Map

Inside main add var headers = {'content-type': 'application/json', 'authorization': 'Bearer xyz123'};. Add print(headers.length);.

Show example solution

void main() {
  var headers = {
    'content-type': 'application/json',
    'authorization': 'Bearer xyz123',
  };
  print(headers.length);
}

Test yourself

What does the Authorization header carry?
- Body
- Token/identity
- URL
- Method
Show answer

Token/identity — the authorization header carries token/identity.
Match the headers

content-type

Body type
authorization

Token
accept

Expected type
cache-control

Cache

Bearer token header

var headers = {'authorization': '____ $token'};

Show answer

var headers = {'authorization': 'Bearer $token'};

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