[Bug-wget] Wget cannot validate https://ftp.gnu.org?

[Jeffrey Walton]

I'm having trouble downloading tarballs from ftp.gnu.org using wget.

wget --ca-certificate="$HOME/.cacert/lets-encrypt-root-x3.pem"
"https://ftp.gnu.org/gnu/libunistring/libunistring-0.9.7.tar.gz"; -O
libunistring-0.9.7.tar.gz
--2017-10-14 17:59:40--
https://ftp.gnu.org/gnu/libunistring/libunistring-0.9.7.tar.gz
Resolving ftp.gnu.org (ftp.gnu.org)... 208.118.235.20, 2001:4830:134:3::b
Connecting to ftp.gnu.org (ftp.gnu.org)|208.118.235.20|:443... connected.
ERROR: cannot verify ftp.gnu.org's certificate, issued by 'CN=Let\'s
Encrypt Authority X3,O=Let\'s Encrypt,C=US':
  unable to get issuer certificate
To connect to ftp.gnu.org insecurely, use `--no-check-certificate'.

The CA file lets-encrypt-root-x3.pem is provided at
https://letsencrypt.org/certs/lets-encrypt-x3-cross-signed.pem.txt,
and it is shown below. It has the CA bit set, basic constraints are
present, and proper key usage are present. It appears to be a valid ca
cert.

The thing that looks unusual to me is, the addition of characters in
the distinguished name. For example, it appears Wget add a slash to
escape the single apostrophe in the common name.

Does anyone have an idea what I might be doing wrong? Or if things are
working as expected, then how do I use the certificate to download the
file using Wget?

**********

$ wget -V
GNU Wget 1.19.1 built on solaris2.11.

-cares +digest -gpgme +https +ipv6 +iri +large-file -metalink +nls
+ntlm +opie -psl +ssl/openssl

Wgetrc:
    /usr/local/etc/wgetrc (system)
Locale:
    /usr/local/share/locale
Compile:
    gcc -DHAVE_CONFIG_H -DSYSTEM_WGETRC="/usr/local/etc/wgetrc"
    -DLOCALEDIR="/usr/local/share/locale" -I. -I../lib -I../lib
    -I/usr/local/include -DNDEBUG -D_REENTRANT -I/usr/include/pcre
    -DNDEBUG -m64
Link:
    gcc -I/usr/include/pcre -DNDEBUG -m64 -m64
    -Wl,-rpath,/usr/local/lib64 -L/usr/local/lib64 -lpcre -luuid -lidn2
    /usr/local/lib64/libssl.so /usr/local/lib64/libcrypto.so
    -R/usr/local/lib64 -ldl -lz -lssl -lcrypto -ldl -lpthread
    ftp-opie.o openssl.o http-ntlm.o ../lib/libgnu.a -lsocket -lnsl
    -lnsl -lnsl -lsocket -lsocket /usr/local/lib64/libiconv.so
    -R/usr/local/lib64 /usr/local/lib64/libunistring.so
    /usr/local/lib64/libiconv.so -ldl -lpthread -R/usr/local/lib64
    -lsocket

**********

$ openssl x509 -in $HOME/cacert/lets-encrypt-root-x3.pem -text -noout
Certificate:
    Data:
        Version: 3 (0x2)
        Serial Number:
            0a:01:41:42:00:00:01:53:85:73:6a:0b:85:ec:a7:08
    Signature Algorithm: sha256WithRSAEncryption
        Issuer: O=Digital Signature Trust Co., CN=DST Root CA X3
        Validity
            Not Before: Mar 17 16:40:46 2016 GMT
            Not After : Mar 17 16:40:46 2021 GMT
        Subject: C=US, O=Let's Encrypt, CN=Let's Encrypt Authority X3
        Subject Public Key Info:
            Public Key Algorithm: rsaEncryption
                Public-Key: (2048 bit)
                Modulus:
                    00:9c:d3:0c:f0:5a:e5:2e:47:b7:72:5d:37:83:b3:
                    68:63:30:ea:d7:35:26:19:25:e1:bd:be:35:f1:70:
                    92:2f:b7:b8:4b:41:05:ab:a9:9e:35:08:58:ec:b1:
                    2a:c4:68:87:0b:a3:e3:75:e4:e6:f3:a7:62:71:ba:
                    79:81:60:1f:d7:91:9a:9f:f3:d0:78:67:71:c8:69:
                    0e:95:91:cf:fe:e6:99:e9:60:3c:48:cc:7e:ca:4d:
                    77:12:24:9d:47:1b:5a:eb:b9:ec:1e:37:00:1c:9c:
                    ac:7b:a7:05:ea:ce:4a:eb:bd:41:e5:36:98:b9:cb:
                    fd:6d:3c:96:68:df:23:2a:42:90:0c:86:74:67:c8:
                    7f:a5:9a:b8:52:61:14:13:3f:65:e9:82:87:cb:db:
                    fa:0e:56:f6:86:89:f3:85:3f:97:86:af:b0:dc:1a:
                    ef:6b:0d:95:16:7d:c4:2b:a0:65:b2:99:04:36:75:
                    80:6b:ac:4a:f3:1b:90:49:78:2f:a2:96:4f:2a:20:
                    25:29:04:c6:74:c0:d0:31:cd:8f:31:38:95:16:ba:
                    a8:33:b8:43:f1:b1:1f:c3:30:7f:a2:79:31:13:3d:
                    2d:36:f8:e3:fc:f2:33:6a:b9:39:31:c5:af:c4:8d:
                    0d:1d:64:16:33:aa:fa:84:29:b6:d4:0b:c0:d8:7d:
                    c3:93
                Exponent: 65537 (0x10001)
        X509v3 extensions:
            X509v3 Basic Constraints: critical
                CA:TRUE, pathlen:0
            X509v3 Key Usage: critical
                Digital Signature, Certificate Sign, CRL Sign
            Authority Information Access:
                OCSP - URI:http://isrg.trustid.ocsp.identrust.com
                CA Issuers - URI:http://apps.identrust.com/roots/dstrootcax3.p7c

            X509v3 Authority Key Identifier:

keyid:C4:A7:B1:A4:7B:2C:71:FA:DB:E1:4B:90:75:FF:C4:15:60:85:89:10

            X509v3 Certificate Policies:
                Policy: 2.23.140.1.2.1
                Policy: 1.3.6.1.4.1.44947.1.1.1
                  CPS: http://cps.root-x1.letsencrypt.org

            X509v3 CRL Distribution Points:

                Full Name:
                  URI:http://crl.identrust.com/DSTROOTCAX3CRL.crl

            X509v3 Subject Key Identifier:
                A8:4A:6A:63:04:7D:DD:BA:E6:D1:39:B7:A6:45:65:EF:F3:A8:EC:A1
    Signature Algorithm: sha256WithRSAEncryption
         dd:33:d7:11:f3:63:58:38:dd:18:15:fb:09:55:be:76:56:b9:
         70:48:a5:69:47:27:7b:c2:24:08:92:f1:5a:1f:4a:12:29:37:
         24:74:51:1c:62:68:b8:cd:95:70:67:e5:f7:a4:bc:4e:28:51:
         cd:9b:e8:ae:87:9d:ea:d8:ba:5a:a1:01:9a:dc:f0:dd:6a:1d:
         6a:d8:3e:57:23:9e:a6:1e:04:62:9a:ff:d7:05:ca:b7:1f:3f:
         c0:0a:48:bc:94:b0:b6:65:62:e0:c1:54:e5:a3:2a:ad:20:c4:
         e9:e6:bb:dc:c8:f6:b5:c3:32:a3:98:cc:77:a8:e6:79:65:07:
         2b:cb:28:fe:3a:16:52:81:ce:52:0c:2e:5f:83:e8:d5:06:33:
         fb:77:6c:ce:40:ea:32:9e:1f:92:5c:41:c1:74:6c:5b:5d:0a:
         5f:33:cc:4d:9f:ac:38:f0:2f:7b:2c:62:9d:d9:a3:91:6f:25:
         1b:2f:90:b1:19:46:3d:f6:7e:1b:a6:7a:87:b9:a3:7a:6d:18:
         fa:25:a5:91:87:15:e0:f2:16:2f:58:b0:06:2f:2c:68:26:c6:
         4b:98:cd:da:9f:0c:f9:7f:90:ed:43:4a:12:44:4e:6f:73:7a:
         28:ea:a4:aa:6e:7b:4c:7d:87:dd:e0:c9:02:44:a7:87:af:c3:
         34:5b:b4:42