There are several ways to do this:

• For a single request:

  let config = {
    headers: {
      header1: value,
    }
  }
  
  let data = {
    'HTTP_CONTENT_LANGUAGE': self.language
  }
  
  axios.post(URL, data, config).then(...)
  

• For setting default global config:

  axios.defaults.headers.post['header1'] = 'value' // for POST requests
  axios.defaults.headers.common['header1'] = 'value' // for all requests
  

• For setting as default on axios instance:

  let instance = axios.create({
    headers: {
      post: {        // can be common or any other method
        header1: 'value1'
      }
    }
  })
  
  //- or after instance has been created
  instance.defaults.headers.post['header1'] = 'value'
  
  //- or before a request is made
  // using Interceptors
  instance.interceptors.request.use(config => {
    config.headers.post['header1'] = 'value';
    return config;
  });
  

You can send a get request with Headers (for authentication with jwt for example):

axios.get('https://example.com/getSomething', {
 headers: {
   Authorization: 'Bearer ' + token //the token is a variable which holds the token
 }
})

Also you can send a post request.

axios.post('https://example.com/postSomething', {
 email: varEmail, //varEmail is a variable which holds the email
 password: varPassword
},
{
  headers: {
    Authorization: 'Bearer ' + varToken
  }
})

My way of doing it,is to set a request like this:

 axios({
  method: 'post', //you can set what request you want to be
  url: 'https://example.com/request',
  data: {id: varID},
  headers: {
    Authorization: 'Bearer ' + varToken
  }
})