net/tlsdial: bake in LetsEncrypt's ISRG Root X1 root
We still try the host's x509 roots first, but if that fails (like if the host is old), we fall back to using LetsEncrypt's root and retrying with that. tlsdial was used in the three main places: logs, control, DERP. But it was missing in dnsfallback. So added it there too, so we can run fine now on a machine with no DNS config and no root CAs configured. Also, move SSLKEYLOGFILE support out of DERP. tlsdial is the logical place for that support. Fixes #1609 Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
This commit is contained in:
Brad Fitzpatrick
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Brad Fitzpatrick
Brad Fitzpatrick
parent
b10a55e4ed
commit
7cf8ec8108
@ -15,9 +15,24 @@ import (
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"crypto/tls"
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"crypto/x509"
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"errors"
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"log"
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"os"
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"strconv"
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"sync"
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"sync/atomic"
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"time"
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)
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var counterFallbackOK int32 // atomic
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// If SSLKEYLOGFILE is set, it's a file to which we write our TLS private keys
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// in a way that WireShark can read.
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//
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// See https://developer.mozilla.org/en-US/docs/Mozilla/Projects/NSS/Key_Log_Format
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var sslKeyLogFile = os.Getenv("SSLKEYLOGFILE")
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var debug, _ = strconv.ParseBool(os.Getenv("TS_DEBUG_TLS_DIAL"))
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// Config returns a tls.Config for connecting to a server.
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// If base is non-nil, it's cloned as the base config before
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// being configured and returned.
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@ -30,11 +45,65 @@ func Config(host string, base *tls.Config) *tls.Config {
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}
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conf.ServerName = host
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if n := sslKeyLogFile; n != "" {
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f, err := os.OpenFile(n, os.O_CREATE|os.O_APPEND|os.O_WRONLY, 0600)
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if err != nil {
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log.Fatal(err)
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}
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log.Printf("WARNING: writing to SSLKEYLOGFILE %v", n)
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conf.KeyLogWriter = f
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}
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if conf.InsecureSkipVerify {
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panic("unexpected base.InsecureSkipVerify")
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}
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if conf.VerifyConnection != nil {
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panic("unexpected base.VerifyConnection")
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}
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// Set InsecureSkipVerify to prevent crypto/tls from doing its
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// own cert verification, as do the same work that it'd do
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// (with the baked-in fallback root) in the VerifyConnection hook.
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conf.InsecureSkipVerify = true
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conf.VerifyConnection = func(cs tls.ConnectionState) error {
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// First try doing x509 verification with the system's
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// root CA pool.
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opts := x509.VerifyOptions{
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DNSName: cs.ServerName,
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Intermediates: x509.NewCertPool(),
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}
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for _, cert := range cs.PeerCertificates[1:] {
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opts.Intermediates.AddCert(cert)
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}
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_, errSys := cs.PeerCertificates[0].Verify(opts)
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if debug {
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log.Printf("tlsdial(sys %q): %v", host, errSys)
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}
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if errSys == nil {
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return nil
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}
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// If that failed, because the system's CA roots are old
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// or broken, fall back to trying LetsEncrypt at least.
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opts.Roots = bakedInRoots()
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_, err := cs.PeerCertificates[0].Verify(opts)
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if debug {
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log.Printf("tlsdial(bake %q): %v", host, err)
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}
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if err == nil {
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atomic.AddInt32(&counterFallbackOK, 1)
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return nil
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}
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return errSys
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}
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return conf
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}
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// SetConfigExpectedCert modifies c to expect and verify that the server returns
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// a certificate for the provided certDNSName.
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//
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// This is for user-configurable client-side domain fronting support,
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// where we send one SNI value but validate a different cert.
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func SetConfigExpectedCert(c *tls.Config, certDNSName string) {
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if c.ServerName == certDNSName {
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return
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@ -50,6 +119,7 @@ func SetConfigExpectedCert(c *tls.Config, certDNSName string) {
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// own cert verification, but do the same work that it'd do
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// (but using certDNSName) in the VerifyPeerCertificate hook.
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c.InsecureSkipVerify = true
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c.VerifyConnection = nil
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c.VerifyPeerCertificate = func(rawCerts [][]byte, _ [][]*x509.Certificate) error {
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if len(rawCerts) == 0 {
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return errors.New("no certs presented")
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@ -70,7 +140,102 @@ func SetConfigExpectedCert(c *tls.Config, certDNSName string) {
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for _, cert := range certs[1:] {
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opts.Intermediates.AddCert(cert)
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}
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_, errSys := certs[0].Verify(opts)
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if debug {
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log.Printf("tlsdial(sys %q/%q): %v", c.ServerName, certDNSName, errSys)
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}
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if errSys == nil {
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return nil
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}
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opts.Roots = bakedInRoots()
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_, err := certs[0].Verify(opts)
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return err
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if debug {
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log.Printf("tlsdial(bake %q/%q): %v", c.ServerName, certDNSName, err)
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}
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if err == nil {
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return nil
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}
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return errSys
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}
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}
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/*
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letsEncryptX1 is the LetsEncrypt X1 root:
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Certificate:
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Data:
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Version: 3 (0x2)
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Serial Number:
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82:10:cf:b0:d2:40:e3:59:44:63:e0:bb:63:82:8b:00
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Signature Algorithm: sha256WithRSAEncryption
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Issuer: C = US, O = Internet Security Research Group, CN = ISRG Root X1
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Validity
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Not Before: Jun 4 11:04:38 2015 GMT
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Not After : Jun 4 11:04:38 2035 GMT
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Subject: C = US, O = Internet Security Research Group, CN = ISRG Root X1
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Subject Public Key Info:
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Public Key Algorithm: rsaEncryption
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RSA Public-Key: (4096 bit)
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We bake it into the binary as a fallback verification root,
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in case the system we're running on doesn't have it.
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(Tailscale runs on some ancient devices.)
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To test that this code is working on Debian/Ubuntu:
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$ sudo mv /usr/share/ca-certificates/mozilla/ISRG_Root_X1.crt{,.old}
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$ sudo update-ca-certificates
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Then restart tailscaled. To also test dnsfallback's use of it, nuke
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your /etc/resolv.conf and it should still start & run fine.
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*/
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const letsEncryptX1 = `
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-----BEGIN CERTIFICATE-----
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MIIFazCCA1OgAwIBAgIRAIIQz7DSQONZRGPgu2OCiwAwDQYJKoZIhvcNAQELBQAw
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TzELMAkGA1UEBhMCVVMxKTAnBgNVBAoTIEludGVybmV0IFNlY3VyaXR5IFJlc2Vh
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cmNoIEdyb3VwMRUwEwYDVQQDEwxJU1JHIFJvb3QgWDEwHhcNMTUwNjA0MTEwNDM4
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WhcNMzUwNjA0MTEwNDM4WjBPMQswCQYDVQQGEwJVUzEpMCcGA1UEChMgSW50ZXJu
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ZXQgU2VjdXJpdHkgUmVzZWFyY2ggR3JvdXAxFTATBgNVBAMTDElTUkcgUm9vdCBY
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MTCCAiIwDQYJKoZIhvcNAQEBBQADggIPADCCAgoCggIBAK3oJHP0FDfzm54rVygc
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h77ct984kIxuPOZXoHj3dcKi/vVqbvYATyjb3miGbESTtrFj/RQSa78f0uoxmyF+
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0TM8ukj13Xnfs7j/EvEhmkvBioZxaUpmZmyPfjxwv60pIgbz5MDmgK7iS4+3mX6U
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A5/TR5d8mUgjU+g4rk8Kb4Mu0UlXjIB0ttov0DiNewNwIRt18jA8+o+u3dpjq+sW
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T8KOEUt+zwvo/7V3LvSye0rgTBIlDHCNAymg4VMk7BPZ7hm/ELNKjD+Jo2FR3qyH
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B5T0Y3HsLuJvW5iB4YlcNHlsdu87kGJ55tukmi8mxdAQ4Q7e2RCOFvu396j3x+UC
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B5iPNgiV5+I3lg02dZ77DnKxHZu8A/lJBdiB3QW0KtZB6awBdpUKD9jf1b0SHzUv
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KBds0pjBqAlkd25HN7rOrFleaJ1/ctaJxQZBKT5ZPt0m9STJEadao0xAH0ahmbWn
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OlFuhjuefXKnEgV4We0+UXgVCwOPjdAvBbI+e0ocS3MFEvzG6uBQE3xDk3SzynTn
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jh8BCNAw1FtxNrQHusEwMFxIt4I7mKZ9YIqioymCzLq9gwQbooMDQaHWBfEbwrbw
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qHyGO0aoSCqI3Haadr8faqU9GY/rOPNk3sgrDQoo//fb4hVC1CLQJ13hef4Y53CI
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rU7m2Ys6xt0nUW7/vGT1M0NPAgMBAAGjQjBAMA4GA1UdDwEB/wQEAwIBBjAPBgNV
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HRMBAf8EBTADAQH/MB0GA1UdDgQWBBR5tFnme7bl5AFzgAiIyBpY9umbbjANBgkq
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hkiG9w0BAQsFAAOCAgEAVR9YqbyyqFDQDLHYGmkgJykIrGF1XIpu+ILlaS/V9lZL
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ubhzEFnTIZd+50xx+7LSYK05qAvqFyFWhfFQDlnrzuBZ6brJFe+GnY+EgPbk6ZGQ
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3BebYhtF8GaV0nxvwuo77x/Py9auJ/GpsMiu/X1+mvoiBOv/2X/qkSsisRcOj/KK
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NFtY2PwByVS5uCbMiogziUwthDyC3+6WVwW6LLv3xLfHTjuCvjHIInNzktHCgKQ5
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ORAzI4JMPJ+GslWYHb4phowim57iaztXOoJwTdwJx4nLCgdNbOhdjsnvzqvHu7Ur
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TkXWStAmzOVyyghqpZXjFaH3pO3JLF+l+/+sKAIuvtd7u+Nxe5AW0wdeRlN8NwdC
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jNPElpzVmbUq4JUagEiuTDkHzsxHpFKVK7q4+63SM1N95R1NbdWhscdCb+ZAJzVc
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oyi3B43njTOQ5yOf+1CceWxG1bQVs5ZufpsMljq4Ui0/1lvh+wjChP4kqKOJ2qxq
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4RgqsahDYVvTH9w7jXbyLeiNdd8XM2w9U/t7y0Ff/9yi0GE44Za4rF2LN9d11TPA
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mRGunUHBcnWEvgJBQl9nJEiU0Zsnvgc/ubhPgXRR4Xq37Z0j4r7g1SgEEzwxA57d
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emyPxgcYxn/eR44/KJ4EBs+lVDR3veyJm+kXQ99b21/+jh5Xos1AnX5iItreGCc=
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-----END CERTIFICATE-----
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`
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var bakedInRootsOnce struct {
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sync.Once
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p *x509.CertPool
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}
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func bakedInRoots() *x509.CertPool {
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bakedInRootsOnce.Do(func() {
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p := x509.NewCertPool()
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if !p.AppendCertsFromPEM([]byte(letsEncryptX1)) {
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panic("bogus PEM")
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}
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bakedInRootsOnce.p = p
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})
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return bakedInRootsOnce.p
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}
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