URI authority

The authority of a URI is the section that comes after the scheme and before the path. It may have up to three parts: user information, host, and port.

Syntax

host
host:port
user@host
user@host:port

• host

  • : The host is usually the domain name or IP address of the server hosting the resource. The domain name is resolved to an IP address using the {{glossary("DNS", "Domain Name System")}} .

• port {{optional_inline}} 

  • : The port is a number that indicates the port on which the server is listening for requests. It is optional and defaults to 80 for HTTP and 443 for HTTPS. Other schemes may define their own defaults or make it mandatory.

• user {{optional_inline}} 

  • : The user is optional and is used for authentication purposes. It is not commonly used in web URIs.

    [!WARNING] Providing user information directly in HTTP URLs is not recommended, as it can expose sensitive information. Use other methods like HTTP authentication or session cookies instead. Sometimes, phishing sites trick users by displaying misleading URLs whose “user” part appears as if it’s a domain name, known as semantic URL attack.

Description

Consider the following URL:

http://www.example.com:80/path/to/myfile.html?key1=value1&key2=value2#SomewhereInTheDocument

The authority in this case is www.example.com:80, comprised of the host name (specifically a domain name) and a port.

www.example.com is the host name of the URI, indicating which Web server is being requested. Here, we use a domain name, but it’s also possible to use an {{Glossary("IP address")}}  of the host. Because IP addresses are less convenient and harder to remember, it’s more common to use a domain name unless the server doesn’t have one registered.

:80 is the port of the URL, indicating the technical “gate” used to access the resources on the web server. It is usually omitted if the web server uses the standard ports of the HTTP protocol (80 for HTTP and 443 for HTTPS) to grant access to its resources. Otherwise, it is mandatory.

Examples

• https://developer.mozilla.org
  • : The host is developer.mozilla.org. The port is not specified but will default to 443 if accessed via https:.
• http://localhost:8080
  • : The host is localhost and the port is 8080. localhost is a special host name that the browser resolves to the local address 127.0.0.1.
• postgresql://postgres:admin123@db:5432
  • : The host is db, and the port is 5432. It also specifies a user postgres and its password admin123. This can be used to connect to a PostgreSQL database.
• https://cnn.example.com&story=breaking_news@10.0.0.1
  • : A misleading URL that looks like it’s pointing to a trusted website. However, the host name is 10.0.0.1, and the cnn.example.com&story=breaking_news part is the “user”.

Specifications

{{Specifications}} 

See also

• URIs
• Choosing between www and non-www URLs