Merge branch 'mc/credential-helper-www-authenticate'

Allow information carried on the WWW-AUthenticate header to be
passed to the credential helpers.

* mc/credential-helper-www-authenticate:
  credential: add WWW-Authenticate header to cred requests
  http: read HTTP WWW-Authenticate response headers
  t5563: add tests for basic and anoymous HTTP access

http.c

@@ -182,6 +182,115 @@ size_t fwrite_buffer(char *ptr, size_t eltsize, size_t nmemb, void *buffer_)
 	return nmemb;
 }
 
+/*
+ * A folded header continuation line starts with any number of spaces or
+ * horizontal tab characters (SP or HTAB) as per RFC 7230 section 3.2.
+ * It is not a continuation line if the line starts with any other character.
+ */
+static inline int is_hdr_continuation(const char *ptr, const size_t size)
+{
+	return size && (*ptr == ' ' || *ptr == '\t');
+}
+
+static size_t fwrite_wwwauth(char *ptr, size_t eltsize, size_t nmemb, void *p)
+{
+	size_t size = eltsize * nmemb;
+	struct strvec *values = &http_auth.wwwauth_headers;
+	struct strbuf buf = STRBUF_INIT;
+	const char *val;
+	size_t val_len;
+
+	/*
+	 * Header lines may not come NULL-terminated from libcurl so we must
+	 * limit all scans to the maximum length of the header line, or leverage
+	 * strbufs for all operations.
+	 *
+	 * In addition, it is possible that header values can be split over
+	 * multiple lines as per RFC 7230. 'Line folding' has been deprecated
+	 * but older servers may still emit them. A continuation header field
+	 * value is identified as starting with a space or horizontal tab.
+	 *
+	 * The formal definition of a header field as given in RFC 7230 is:
+	 *
+	 * header-field   = field-name ":" OWS field-value OWS
+	 *
+	 * field-name     = token
+	 * field-value    = *( field-content / obs-fold )
+	 * field-content  = field-vchar [ 1*( SP / HTAB ) field-vchar ]
+	 * field-vchar    = VCHAR / obs-text
+	 *
+	 * obs-fold       = CRLF 1*( SP / HTAB )
+	 *                ; obsolete line folding
+	 *                ; see Section 3.2.4
+	 */
+
+	/* Start of a new WWW-Authenticate header */
+	if (skip_iprefix_mem(ptr, size, "www-authenticate:", &val, &val_len)) {
+		strbuf_add(&buf, val, val_len);
+
+		/*
+		 * Strip the CRLF that should be present at the end of each
+		 * field as well as any trailing or leading whitespace from the
+		 * value.
+		 */
+		strbuf_trim(&buf);
+
+		strvec_push(values, buf.buf);
+		http_auth.header_is_last_match = 1;
+		goto exit;
+	}
+
+	/*
+	 * This line could be a continuation of the previously matched header
+	 * field. If this is the case then we should append this value to the
+	 * end of the previously consumed value.
+	 */
+	if (http_auth.header_is_last_match && is_hdr_continuation(ptr, size)) {
+		/*
+		 * Trim the CRLF and any leading or trailing from this line.
+		 */
+		strbuf_add(&buf, ptr, size);
+		strbuf_trim(&buf);
+
+		/*
+		 * At this point we should always have at least one existing
+		 * value, even if it is empty. Do not bother appending the new
+		 * value if this continuation header is itself empty.
+		 */
+		if (!values->nr) {
+			BUG("should have at least one existing header value");
+		} else if (buf.len) {
+			char *prev = xstrdup(values->v[values->nr - 1]);
+
+			/* Join two non-empty values with a single space. */
+			const char *const sp = *prev ? " " : "";
+
+			strvec_pop(values);
+			strvec_pushf(values, "%s%s%s", prev, sp, buf.buf);
+			free(prev);
+		}
+
+		goto exit;
+	}
+
+	/* Not a continuation of a previously matched auth header line. */
+	http_auth.header_is_last_match = 0;
+
+	/*
+	 * If this is a HTTP status line and not a header field, this signals
+	 * a different HTTP response. libcurl writes all the output of all
+	 * response headers of all responses, including redirects.
+	 * We only care about the last HTTP request response's headers so clear
+	 * the existing array.
+	 */
+	if (skip_iprefix_mem(ptr, size, "http/", &val, &val_len))
+		strvec_clear(values);
+
+exit:
+	strbuf_release(&buf);
+	return size;
+}
+
 size_t fwrite_null(char *ptr, size_t eltsize, size_t nmemb, void *strbuf)
 {
 	return nmemb;
@@ -1896,6 +2005,8 @@ static int http_request(const char *url,
 					 fwrite_buffer);
 	}
 
+	curl_easy_setopt(slot->curl, CURLOPT_HEADERFUNCTION, fwrite_wwwauth);
+
 	accept_language = http_get_accept_language_header();
 
 	if (accept_language)