I tried to sign some data from the openstack/keystone project with:

$ xmlsec1 --sign --privkey-pem
examples/pki/private/signing_key.pem,examples/pki/certs/signing_cert.pem
--id-attr:ID Assertion /tmp/xxx
func=xmlSecCryptoDLLibraryCreate:file=dl.c:line=146:obj=lt_dlopenext:subj=unknown:error=7:io
function failed:filename=libxmlsec1-openssl
func=xmlSecCryptoDLGetLibraryFunctions:file=dl.c:line=499:obj=unknown:subj=xmlSecCryptoDLLibraryCreate:error=1:xmlsec
library function failed:crypto=openssl
func=xmlSecCryptoDLLoadLibrary:file=dl.c:line=449:obj=unknown:subj=xmlSecCryptoDLGetLibraryFunctions:error=1:xmlsec
library function failed: 
Error: unable to load xmlsec-openssl library. Make sure that you have
this it installed, check shared libraries path (LD_LIBRARY_PATH)
envornment variable or use "--crypto" option to specify different
crypto engine.
Error: initialization failed
Usage: xmlsec <command> [<options>] [<files>]

xmlsec is a command line tool for signing, verifying, encrypting and
decrypting XML documents. The allowed <command> values are:
  --help          display this help information and exit
  --help-all      display help information for all commands/options and exit
  --help-<cmd>    display help information for command <cmd> and exit
  --version       print version information and exit
  --keys          keys XML file manipulation
  --sign          sign data and output XML document
  --verify        verify signed document
  --sign-tmpl     create and sign dynamicaly generated signature template
  --encrypt       encrypt data and output XML document
  --decrypt       decrypt data from XML document


Report bugs to http://www.aleksey.com/xmlsec/bugs.html

Written by Aleksey Sanin <aleksey@aleksey.com>.

Copyright (C) 2002-2016 Aleksey Sanin <aleksey@aleksey.com>. All Rights
Reserved..
This is free software: see the source for copying information.

func=xmlSecCryptoShutdown:file=app.c:line=69:obj=unknown:subj=cryptoShutdown:error=9:feature
is not implemented: 
func=xmlSecAppCryptoShutdown:file=crypto.c:line=48:obj=unknown:subj=xmlSecCryptoShutdown:error=1:xmlsec
library function failed: 
Error: xmlsec crypto shutdown failed.


Looks like the library can not be found. But I have it installed:

S | Name                | Type    | Version    | Arch   | Repository           
--+---------------------+---------+------------+--------+----------------------
i | libxmlsec1-1        | package | 1.2.22-2.3 | x86_64 | Main Repository (OSS)
i | libxmlsec1-openssl1 | package | 1.2.22-2.3 | x86_64 | Main Repository (OSS)
i | xmlsec1             | package | 1.2.22-2.3 | x86_64 | Main Repository (OSS)