When using --negotiate with curl, is a keytab file required? - hadoop

Question

The documentation describing how to connect to a kerberos secured endpoint shows the following:
curl -i --negotiate -u : "http://<HOST>:<PORT>/webhdfs/v1/<PATH>?op=..."
The -u flag has to be provided but is ignored by curl.
Does the --negotiate option cause curl to look for a keytab that was created beforehand with the kinit command, or will curl prompt for credentials?
If it looks for a keytab file, what filename will the command be looking for?

Answer 1

Being a once-in-a-while-contributor to curl in that area. Here is what you need to know:
curl(1) itself knows nothing about Kerberos and will not interact neither with your credential cache nor your keytab file. It will delegate all calls to a GSS-API implementation which will do the magic for you. What magic depends on the library, Heimdal and MIT Kerberos.
Based on your question, I assume that you have little knowledge about Kerberos and want simply automate API calls to a REST endpoints secured by SPNEGO.
Here is what you need to do:
Have a Unix-like OS
Install at least MIT Kerberos 1.11
Install at least curl 7.38.0 against MIT Kerberos
Verify this with curl --version mentioning GSS-API and SPNEGO and with ldd linked against your MIT Kerberos version.
Create a client keytab for the service principal with ktutil or mskutil
Try to obtain a TGT with that client keytab by kinit -k -t <path-to-keytab> <principal-from-keytab>
Verify with klist that you have a ticket cache
Environment is now ready to go:
Export KRB5CCNAME=<some-non-default-path>
Export KRB5_CLIENT_KTNAME=<path-to-keytab>
Invoke curl --negotiate -u : <URL>
MIT Kerberos will detect that both environment variables are set, inspect them, automatically obtain a TGT with your keytab, request a service ticket and pass to curl. You are done.
Note: this will not work with Heimdal.

Answer 2

Check curl version
$ curl -V - It should support the feature "GSS-Negotiate"
Login using kinit
$ kinit <user-id>
Use curl
$ curl --negotiate -u : -b ~/cookiejar.txt -c ~/cookiejar.txt http://localhost:14000/webhdfs/v1/?op=liststatus
"--negotiate" option enables SPNEGO
"-u" option is required but ignored (the principle specified during kinit is used)
"-b" & "-c" options are used to store and send http cookies.

Answer 3

I am using version 7.54.0. The following command works fine for me. (please remember/pay attention there are double dashes before the negotiate option).
curl --negotiate -u: '<the_full_url>'