Why Does Basic HTTP Authentication Fail in Go When Redirects Occur?

Basic HTTP Authentication Handling in Go

When implementing basic HTTP authentication in Go, some unexpected challenges may arise. This article delves into a common issue encountered when attempting to implement basic HTTP authentication.

Issue: An error stating "unsupported protocol scheme" is encountered when executing the following code:

func basicAuth() string {
    var username string = "foo"
    var passwd string = "bar"
    client := &http.Client{}
    req, err := http.NewRequest("GET", "mydomain.example", nil)
    req.SetBasicAuth(username, passwd)
    resp, err := client.Do(req)
    if err != nil{
        log.Fatal(err)
    }
    bodyText, err := ioutil.ReadAll(resp.Body)
    s := string(bodyText)
    return s
}

Cause: When redirects occur, Go-lang discards any specified headers, including the Authorization header set for basic authentication.

Solution: To rectify this issue, a custom redirect policy function can be implemented:

func redirectPolicyFunc(req *http.Request, via []*http.Request) error {
    req.Header.Add("Authorization", "Basic "+basicAuth("username1", "password123"))
    return nil
}

This function ensures that the Authorization header is added back during redirects, effectively preserving the authentication credentials.

Implementation:

func main() {
    client := &http.Client{
        Jar: cookieJar,
        CheckRedirect: redirectPolicyFunc,
    }
    req, err := http.NewRequest("GET", "http://localhost/", nil)
    req.Header.Add("Authorization", "Basic "+basicAuth("username1", "password123")) 
    resp, err := client.Do(req)
}

By utilizing the redirect policy function, the specified headers, including the Authorization header for basic authentication, will persist throughout redirects, ensuring successful authentication with the target server.

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