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libcurl library is single monolithic binary with multiple optional protocols and features. Some of binary packages are build with all features enabled but it's unknown for CMake user. Simple find_package(CURL) could be not enough to be sure correct libcurl is available and delivers expected features.

Using #18378 approach should enable protocols and additional features listed in libbcurl.pc to be analysed and verified at CMake configuration time.

find_package(CURL COMPONENTS HTTP HTTPS LDAP LDAPS NTLM OPTIONAL_COMPONENTS IPv6 HTTPS-proxy) syntax should be supported - user should be warned if some listed features are missing and error raised if they are required.

Example of libcurl.pc file from Debian:

prefix=/usr
exec_prefix=${prefix}
libdir=${prefix}/lib/x86_64-linux-gnu
includedir=/usr/include/x86_64-linux-gnu
supported_protocols="DICT FILE FTP FTPS GOPHER HTTP HTTPS IMAP IMAPS LDAP LDAPS POP3 POP3S RTMP RTSP SCP SFTP SMB SMBS SMTP SMTPS TELNET TFTP"
supported_features="SSL IPv6 UnixSockets libz AsynchDNS IDN GSS-API PSL SPNEGO Kerberos NTLM NTLM_WB TLS-SRP HTTP2 HTTPS-proxy"

Name: libcurl
URL: https://curl.haxx.se/
Description: Library to transfer files with ftp, http, etc.
Version: 7.52.1
Libs: -L${libdir} -lcurl
Libs.private: -lnghttp2 -lidn2 -lrtmp -lssh2 -lpsl -lssl -lcrypto -lssl -lcrypto -L/usr/lib/x86_64-linux-gnu/mit-krb5 -Wl,-z,relro -lgssapi_krb5 -lkrb5 -lk5crypto -lcom_err -llber -llber -lldap -lz
Cflags: -I${includedir}