Basic Authentication with Fetch?

A solution without dependencies.

Node

headers.set('Authorization', 'Basic ' + Buffer.from(username + ":" + password).toString('base64'));

Browser

headers.set('Authorization', 'Basic ' + btoa(username + ":" + password));

A simple example for copy-pasting into Chrome console:

fetch(' {method:'GET', 
headers: {'Authorization': 'Basic ' + btoa('login:password')}})
.then(response => response.json())
.then(json => console.log(json));

or with await:

let response = await fetch(' {method:'GET', 
headers: {'Authorization': 'Basic ' + btoa('login:password')}});
let data = await response.json();
console.log(data);

In pure JavaScript you can also use btoa instead of base64.encode():

headers.set('Authorization', 'Basic ' + btoa(username + ":" + password));

Note that this will only work with ASCII characters.

If you have to handle different encodings, see the linked btoa documentation.

If you have a backend server asking for the Basic Auth credentials before the app then this is sufficient, it will re-use that then:

fetch(url, {
  credentials: 'include',
}).then(...);

NODE USERS (REACT,EXPRESS) FOLLOW THESE STEPS

1. npm install base-64 --save
2. import { encode } from "base-64";

3.  const response = await fetch(URL, {
     method: 'post',
     headers: new Headers({
       'Authorization': 'Basic ' + encode(username + ":" + password),
       'Content-Type': 'application/json'
     }),
     body: JSON.stringify({
       "PassengerMobile": "xxxxxxxxxxxx",
       "Password": "xxxxxxx"
     })
   });
   const posts = await response.json();
   

4. Don't forget to define this whole function as async

get request with authorization for React Native Mobile application, i have spent more time searching for these lines inside fetch

 var base64 = require("base-64"); // install it before use from npm i base-64

 const uname = "some username goes here";
 const pword = "some password goes here";

const getMovies = async () => {
   try {
     const response = await fetch(
       "API URL goes here",
       {
         headers: {
           Authorization: "Basic " + base64.encode(uname + ":" + pword),
         },
       }
     );

     data = await response.json();
     setData(data);

     console.log(data);
     // console.log(data.name);
     return data;
   } catch (error) {
     console.error(error);
   } finally {
     setLoading(false);
   }
 };

 useEffect(() => {
   getMovies();
 }, []);


// other code 

// inside return
  <FlatList
           keyExtractor={(item) => item.id}
           data={data}
           renderItem={({ item }) => (
             <View style={styles.text_container}>
               <Text>{item.name}</Text>
               <Text>{item.images[0].name}</Text>
               <Text>{item.images[0].src}</Text>
             </View>
           )}
         />

I'll share a code which has Basic Auth Header form data request body,

let username = 'test-name';
let password = 'EbQZB37gbS2yEsfs';
let formdata = new FormData();
let headers = new Headers();


formdata.append('grant_type','password');
formdata.append('username','testname');
formdata.append('password','qawsedrf');

headers.append('Authorization', 'Basic ' + base64.encode(username + ":" + password));
fetch(' {
 method: 'POST',
 headers: headers,
 body: formdata
}).then((response) => response.json())
.then((responseJson) => {
 console.log(responseJson);

 this.setState({
    data: responseJson
 })
  })
   .catch((error) => {
 console.error(error);
   });

This is not directly related to the initial issue, but probably will help somebody.

I faced same issue when was trying to send similar request using domain account. So mine issue was in not escaped character in login name.

Bad example:

'ABC\username'

Good example:

'ABC\\username'