[http] Add support for HTTP Basic authentication

src/net/tcp/http.c

 #include <gpxe/process.h>
 #include <gpxe/linebuf.h>
 #include <gpxe/features.h>
+#include <gpxe/base64.h>
 #include <gpxe/http.h>
 
 FEATURE ( FEATURE_PROTOCOL, "HTTP", DHCP_EB_FEATURE_HTTP, 1 );
 		return -ENOENT;
 	case 403:
 		return -EPERM;
+	case 401:
+		return -EACCES;
 	default:
 		return -EIO;
 	}
 	const char *path = http->uri->path;
 	const char *host = http->uri->host;
 	const char *query = http->uri->query;
+	const char *user = http->uri->user;
+	const char *password = http->uri->password;
+	size_t user_pw_len = ( ( user && password ) ?
+			       ( strlen ( user ) + 1 /* ":" */ +
+				 strlen ( password ) ) : 0 );
+	size_t user_pw_base64_len = base64_encoded_len ( user_pw_len );
+	char user_pw[ user_pw_len + 1 /* NUL */ ];
+	char user_pw_base64[ user_pw_base64_len + 1 /* NUL */ ];
 	int rc;
 
 	if ( xfer_window ( &http->socket ) ) {
+
+		/* We want to execute only once */
 		process_del ( &http->process );
+
+		/* Construct authorisation, if applicable */
+		if ( user_pw_len ) {
+			snprintf ( user_pw, sizeof ( user_pw ), "%s:%s",
+				   user, password );
+			base64_encode ( user_pw, user_pw_base64 );
+		}
+
+		/* Send GET request */
 		if ( ( rc = xfer_printf ( &http->socket,
 					  "GET %s%s%s HTTP/1.0\r\n"
 					  "User-Agent: gPXE/" VERSION "\r\n"
+					  "%s%s%s"
 					  "Host: %s\r\n"
 					  "\r\n",
 					  ( path ? path : "/" ),
 					  ( query ? "?" : "" ),
 					  ( query ? query : "" ),
+					  ( user_pw_len ?
+					    "Authorization: Basic " : "" ),
+					  ( user_pw_len ?
+					    user_pw_base64 : "" ),
+					  ( user_pw_len ? "\r\n" : "" ),
 					  host ) ) != 0 ) {
 			http_done ( http, rc );
 		}