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curl/docs/libcurl
Johannes Schindelin 5450428491 schannel: add "best effort" revocation check option
- Implement new option CURLSSLOPT_REVOKE_BEST_EFFORT and
  --ssl-revoke-best-effort to allow a "best effort" revocation check.

A best effort revocation check ignores errors that the revocation check
was unable to take place. The reasoning is described in detail below and
discussed further in the PR.

---

When running e.g. with Fiddler, the schannel backend fails with an
unhelpful error message:

	Unknown error (0x80092012) - The revocation function was unable
	to check revocation for the certificate.

Sadly, many enterprise users who are stuck behind MITM proxies suffer
the very same problem.

This has been discussed in plenty of issues:
https://github.com/curl/curl/issues/3727,
https://github.com/curl/curl/issues/264, for example.

In the latter, a Microsoft Edge developer even made the case that the
common behavior is to ignore issues when a certificate has no recorded
distribution point for revocation lists, or when the server is offline.
This is also known as "best effort" strategy and addresses the Fiddler
issue.

Unfortunately, this strategy was not chosen as the default for schannel
(and is therefore a backend-specific behavior: OpenSSL seems to happily
ignore the offline servers and missing distribution points).

To maintain backward-compatibility, we therefore add a new flag
(`CURLSSLOPT_REVOKE_BEST_EFFORT`) and a new option
(`--ssl-revoke-best-effort`) to select the new behavior.

Due to the many related issues Git for Windows and GitHub Desktop, the
plan is to make this behavior the default in these software packages.

The test 2070 was added to verify this behavior, adapted from 310.

Based-on-work-by: georgeok <giorgos.n.oikonomou@gmail.com>
Co-authored-by: Markus Olsson <j.markus.olsson@gmail.com>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

Closes https://github.com/curl/curl/pull/4981
2020-03-18 03:23:39 -04:00
..
opts schannel: add "best effort" revocation check option 2020-03-18 03:23:39 -04:00
.gitignore
ABI
CMakeLists.txt
curl_easy_cleanup.3 docs: mention NULL is fine input to several functions 2018-08-10 00:24:12 +02:00
curl_easy_duphandle.3 curl_easy_duphandle.3: clarify that a duped handle has no shares 2019-03-01 21:47:30 +01:00
curl_easy_escape.3
curl_easy_getinfo.3 CURLINFO_RETRY_AFTER: parse the Retry-After header value 2019-08-07 14:45:39 +02:00
curl_easy_init.3
curl_easy_pause.3
curl_easy_perform.3 whitespace fixes 2018-09-23 22:24:02 +00:00
curl_easy_recv.3
curl_easy_reset.3 altsvc: keep a copy of the file name to survive handle reset 2020-02-09 22:41:49 +01:00
curl_easy_send.3
curl_easy_setopt.3 smtp: Allow RCPT TO command to fail for some recipients 2020-01-21 10:40:19 +01:00
curl_easy_strerror.3
curl_easy_unescape.3
curl_easy_upkeep.3 curl_easy_upkeep: removed 'conn' from the name 2018-09-07 13:43:26 +02:00
curl_escape.3 curl_escape.3: Add a link to curl_free 2020-03-02 18:16:24 -05:00
curl_formadd.3 documentation: curl_formadd field and file names are now escaped 2018-12-11 15:31:23 +01:00
curl_formfree.3 docs: mention NULL is fine input to several functions 2018-08-10 00:24:12 +02:00
curl_formget.3 mime: new MIME API. 2017-09-02 17:47:10 +01:00
curl_free.3 docs: mention NULL is fine input to several functions 2018-08-10 00:24:12 +02:00
curl_getdate.3 parsedate: fix date parsing for systems with 32 bit long 2018-01-25 22:20:52 +01:00
curl_getenv.3 curl_getenv.3: Fix the memory handling description 2020-03-02 18:16:23 -05:00
curl_global_cleanup.3
curl_global_init_mem.3 curl_global_init_mem.3: mention it was added in 7.12.0 2019-08-11 00:19:45 +02:00
curl_global_init.3 global_init: assume the EINTR bit by default 2020-01-26 18:27:18 +01:00
curl_global_sslset.3 polarssl: remove more references and mentions 2020-03-05 07:57:45 +01:00
curl_mime_addpart.3 form/mime: field names are not allowed to contain zero-valued bytes. 2017-09-22 01:08:29 +01:00
curl_mime_data_cb.3 docs: fix typos 2018-04-17 15:32:51 -04:00
curl_mime_data.3 form/mime: field names are not allowed to contain zero-valued bytes. 2017-09-22 01:08:29 +01:00
curl_mime_encoder.3 mime: implement encoders. 2017-09-05 17:55:51 +01:00
curl_mime_filedata.3 docs: fix typos 2018-04-17 15:32:51 -04:00
curl_mime_filename.3 form/mime: field names are not allowed to contain zero-valued bytes. 2017-09-22 01:08:29 +01:00
curl_mime_free.3 docs: mention NULL is fine input to several functions 2018-08-10 00:24:12 +02:00
curl_mime_headers.3 form/mime: field names are not allowed to contain zero-valued bytes. 2017-09-22 01:08:29 +01:00
curl_mime_init.3 form/mime: field names are not allowed to contain zero-valued bytes. 2017-09-22 01:08:29 +01:00
curl_mime_name.3 form/mime: field names are not allowed to contain zero-valued bytes. 2017-09-22 01:08:29 +01:00
curl_mime_subparts.3 docs/curl_mime_*.3: added examples 2017-09-05 11:15:02 +02:00
curl_mime_type.3 docs: fix typos 2018-04-17 15:32:51 -04:00
curl_mprintf.3
curl_multi_add_handle.3 docs: fix missed option name markups 2018-06-30 18:33:07 +02:00
curl_multi_assign.3
curl_multi_cleanup.3 docs: mention NULL is fine input to several functions 2018-08-10 00:24:12 +02:00
curl_multi_fdset.3 curl_multi_fdset.3: emphasize curl_multi_timeout 2017-11-09 07:52:19 +01:00
curl_multi_info_read.3
curl_multi_init.3 whitespace fixes 2018-09-23 22:24:02 +00:00
curl_multi_perform.3 copyrights: update all copyright notices to 2019 on files changed this year 2019-11-02 23:15:56 +01:00
curl_multi_poll.3 multi: add curl_multi_wakeup() 2019-11-25 15:45:56 +01:00
curl_multi_remove_handle.3 curl_multi_remove_handle.3: use at any time, just not from within callbacks 2019-02-19 11:22:29 +01:00
curl_multi_setopt.3 CURLMOPT_MAX_CONCURRENT_STREAMS: new setopt 2019-10-02 07:47:48 +02:00
curl_multi_socket_action.3 CURLMOPT_SOCKETFUNCTION.3: clarified 2019-06-10 13:07:32 +02:00
curl_multi_socket_all.3
curl_multi_socket.3 docs: fix missed option name markups 2018-06-30 18:33:07 +02:00
curl_multi_strerror.3
curl_multi_timeout.3 whitespace fixes 2018-09-23 22:24:02 +00:00
curl_multi_wait.3 docs: add more references to curl_multi_poll 2019-11-28 22:29:18 +01:00
curl_multi_wakeup.3 curl_multi_wakeup.3: add example and AVAILABILITY 2019-11-26 08:11:32 +01:00
curl_share_cleanup.3 docs: mention NULL is fine input to several functions 2018-08-10 00:24:12 +02:00
curl_share_init.3 whitespace fixes 2018-09-23 22:24:02 +00:00
curl_share_setopt.3 curl_share_setopt.3: Note sharing cookies doesn't enable the engine 2020-03-06 02:57:17 -05:00
curl_share_strerror.3
curl_slist_append.3 docs: mention potential leak in curl_slist_append 2019-01-02 12:49:49 +01:00
curl_slist_free_all.3 whitespace fixes 2018-09-23 22:24:02 +00:00
curl_strequal.3
curl_strnequal.3
curl_unescape.3
curl_url_cleanup.3 curl_url-docs: fix AVAILABILITY as Added in curl 7.62.0 2018-09-08 16:02:25 +02:00
curl_url_dup.3 curl_url-docs: fix AVAILABILITY as Added in curl 7.62.0 2018-09-08 16:02:25 +02:00
curl_url_get.3 docs: disambiguate CURLUPART_HOST is for host name (ie no port) 2019-09-28 18:13:33 +02:00
curl_url_set.3 docs: mention CURL_MAX_INPUT_LENGTH restrictions 2020-01-05 17:06:47 +01:00
curl_url.3 curl_url.3: this is not experimental anymore 2019-03-22 18:33:06 +01:00
curl_version_info.3 curl_version_info: make the quic_version a const 2019-08-13 23:15:49 +02:00
curl_version.3
getinfo-times
libcurl-easy.3
libcurl-env.3 docs: fix typos 2018-04-17 15:32:51 -04:00
libcurl-errors.3 multi: Improve parameter check for curl_multi_remove_handle 2020-03-18 02:58:42 -04:00
libcurl-multi.3 docs: add more references to curl_multi_poll 2019-11-28 22:29:18 +01:00
libcurl-security.3 docs: add warnings about FILE: URLs on Windows 2020-03-13 16:56:41 +01:00
libcurl-share.3 libcurl-share.3: the connection cache is shareable now 2017-11-27 09:42:39 +01:00
libcurl-thread.3 docs: Fix links to OpenSSL docs 2019-06-30 17:16:28 -04:00
libcurl-tutorial.3 copyrights: update all copyright notices to 2019 on files changed this year 2019-11-02 23:15:56 +01:00
libcurl-url.3 libcurl-url.3: overview man page for the URL API 2018-09-10 23:29:37 +02:00
libcurl.3
libcurl.m4
Makefile.am docs/libcurl/index.html: removed 2018-05-15 16:41:55 +02:00
Makefile.inc multi: add curl_multi_wakeup() 2019-11-25 15:45:56 +01:00
mksymbolsmanpage.pl scripts: allow all perl scripts to be run directly 2018-01-07 15:42:11 -05:00
symbols-in-versions schannel: add "best effort" revocation check option 2020-03-18 03:23:39 -04:00
symbols.pl scripts: allow all perl scripts to be run directly 2018-01-07 15:42:11 -05:00