curl and libcurl 8.21.0

 Public curl releases:         275
 Command line options:         273
 curl_easy_setopt() options:   308
 Public functions in libcurl:  100
 Authors:                      1465
 Contributors:                 3668

This release includes the following changes:

 o lib: drop support for CURLAUTH_DIGEST_IE [4]

This release includes the following bugfixes:

 o asyn-thrdd: fix result processing without wakeup socketpair [2]
 o cmake: auto-select static nghttp2/nghttp3/ngtcp2 Config [8]
 o cmake: fix zstd CMake config name [5]
 o cookie: simplify strstore(), remove outdated comment [12]
 o CURLOPT_ECH.md: simplify the description language [18]
 o CURLOPT_HAPROXYPROTOCOL.md: only sent for newly setup connections [32]
 o ECH: cleanups [20]
 o ftp: avoid accessing EPSV response one byte past the NULL [9]
 o ftp: remove 2 Curl_resolv_blocking() calls [30]
 o ftp: remove bits.ftp_use_control_ssl [28]
 o gtls: fix some typos [15]
 o ldap: fix minor leak on write callback error [24]
 o lib: two minor typos [16]
 o libcurl-easy.md: minor clarifications [19]
 o mbedtls: null terminate the private key blob [36]
 o mqtt: validate PINGRESP and DISCONNECT have remaining_length == 0 [7]
 o schannel_verify: avoid out of blob access [11]
 o setopt: changing the proxy port is also a proxy change [23]
 o setopt: gate a few proxy TLS options by checking backend support [35]
 o show-headers.md: mention bold headers and --no-styled-output [17]
 o tests: fix unit1636 with --disable-progress-meter [37]
 o tool_formparse.c: fix two minor comment typos [25]
 o tool_formparse: polish error message + make two functions static [1]
 o tool_formparse: tool2curlparts is no longer recursive [33]
 o tool_urlglob: avoid overflow at end of range [22]
 o url: fix connection reuse for starttls protocols [27]
 o url: remove ssh_config_matches [31]
 o user-agent.md: mention double quotes too [3]
 o x509asn1: fix operator order in do_pubkey [21]

This release includes the following known bugs:

 See https://curl.se/docs/knownbugs.html

For all changes ever done in curl:

 See https://curl.se/changes.html

Planned upcoming removals include:

 o local crypto implementations
 o NTLM
 o SMB
 o TLS-SRP support

 See https://curl.se/dev/deprecate.html

This release would not have looked like this without help, code, reports and
advice from friends like these:

  Andrew Nesbit, Dan Fandrich, Daniel Stenberg, dependabot[bot], Elise Vance,
  Jeremy Nicoll, Kai Pastor, parasol-aser, Raymond Steen, renovate[bot],
  Sollace on github, Stefan Eissing, Viktor Szakats
  (13 contributors)

References to bug reports and discussions on issues:

 [1] = https://curl.se/bug/?i=21510
 [2] = https://curl.se/bug/?i=21476
 [3] = https://curl.se/mail/archive-2026-04/0029.html
 [4] = https://curl.se/bug/?i=21486
 [5] = https://curl.se/bug/?i=21538
 [7] = https://hackerone.com/reports/3702718
 [8] = https://curl.se/bug/?i=21470
 [9] = https://curl.se/bug/?i=21545
 [11] = https://curl.se/bug/?i=21543
 [12] = https://curl.se/bug/?i=21541
 [15] = https://curl.se/bug/?i=21498
 [16] = https://curl.se/bug/?i=21496
 [17] = https://curl.se/bug/?i=21495
 [18] = https://curl.se/bug/?i=21536
 [19] = https://curl.se/bug/?i=21491
 [20] = https://curl.se/bug/?i=21532
 [21] = https://curl.se/bug/?i=21533
 [22] = https://curl.se/bug/?i=21529
 [23] = https://curl.se/bug/?i=21485
 [24] = https://curl.se/bug/?i=21530
 [25] = https://curl.se/bug/?i=21480
 [27] = https://curl.se/bug/?i=21522
 [28] = https://curl.se/bug/?i=21521
 [30] = https://curl.se/bug/?i=21512
 [31] = https://curl.se/bug/?i=21519
 [32] = https://curl.se/bug/?i=21517
 [33] = https://curl.se/bug/?i=21518
 [35] = https://curl.se/bug/?i=21514
 [36] = https://curl.se/bug/?i=21515
 [37] = https://curl.se/bug/?i=21500
