How to use SPNEGO negotiation with Curl

1. First we need to check that we have an SPNEGO compatible Curl installed:

$ curl -V
curl 7.81.0 (x86_64-w64-mingw32) libcurl/7.81.0 OpenSSL/1.1.1m (Schannel) zlib/1.2.11 brotli/1.0.9 zstd/1.5.2 libidn2/2.3.1 libssh2/1.10.0 nghttp2/1.46.0
Release-Date: 2022-01-05
Protocols: dict file ftp ftps gopher gophers http https imap imaps ldap ldaps mqtt pop3 pop3s rtsp scp sftp smb smbs smtp smtps telnet tftp
Features: alt-svc AsynchDNS brotli HSTS HTTP2 HTTPS-proxy IDN IPv6 Kerberos Largefile libz MultiSSL NTLM SPNEGO SSL SSPI TLS-SRP zstd

Here we can see that the SPNEGO feature is available

2. Next we need to create a credentials cache for Curl to use

kinit <username>
Password for <username>@<domain.com>: <password>

Here we create a “authentication token” and put it in a credentials cache för Curl, and any other program ie. SoapUI and others, to use. ‘username’ is the name of the user. This can be omitted, and if so the default user and domain (user that runs the command) will be used instead. The ‘kinit’ command will ask for the password associated with the user. After this has been inputed the token is created

3. After that we run Curl with the following options:

curl --negotiate -u : https://a-spnego-protected-site/data-i-want-to-access

–negotiate will trigger SPNEGO behaviour
-u is neccessary
: should point to the SPNEGO protected resource we want to access
Curl will now use the token in the credentials chace to authenticate against the web resource

Troubleshooting commands:

klist - lists all current tokens with the expiry timestamps in the cache
kdestroy - remove a ticket from the credentials cache

Tested with Curl v7.81.0 in GitBash on a Windows 10 with Java 1.8.0_301

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