Add support for importing keys into the token as session ephemeral keys

[simo5]

Description

In some circumstances we need to be able to import keys into the token as the caller wants the token to perform the cryptographic operation but provides the keys in PEM files, or BIO objects and does not want to permanently store these keys in the token (for whatever reason).

ECDH is an example where we need to import a key only halfway.

Importing private keys always immediately create a temporary session object on the login session (which is generally long lived). The operation assumes that a login session is already available or a pin is otherwise specified in the configuration. The login session is assumed to be opened on the default slot which is defined as the first slot that fulfill basic session storage writability. In future we may add quirks to specify a different default slot via a uri.

Importing public keys (which may happen more frequently in key exchange situations) creates a mock object by default, however requesting their token handle triggers the storage of the key into the token login session as an ephmeral key, just like for the private keys.
The handle is requested in case an actual operation needs to happen on the token, and does not happen for the ECDH case, this way we avoid littering the login session object with too many throwaway keys.

This PR also addresses some issues with ECDH.

Related #395
Fixes #305
Fixes #437

Checklist

• Code modified for feature
• Test suite updated with functionality tests
• [ ] Test suite updated with negative tests
• [ ] Documentation updated

Reviewer's checklist:

• Any issues marked for closing are addressed
• There is a test suite reasonably covering new functionality or modifications
• This feature/change has adequate documentation added
• Code conform to coding style that today cannot yet be enforced via the check style test
• Commits have short titles and sensible commit messages
• Coverity Scan has run if needed (code PR) and no new defects were found

[simo5]

@kshitizvars please check out this PR

[simo5]

Ubuntu fails genpkey apparently .... that's odd.

[simo5]

Will have to figure out the genpkey cmdline issue for Ubuntu, meanwhile triggering a covscan to ensure the C code is fine.

[simo5]

Older openssl seem to have no support for -outpubkey ...

[simo5]

Coverity found issues, sticking them here so that I do not forget, and marking the PR as draft for now.

New defect(s) Reported-by: Coverity Scan
Showing 3 of 3 defect(s)


** CID 509200:  Error handling issues  (CHECKED_RETURN)
/src/util.c: 831 in p11prov_uri_set_label()


________________________________________________________________________________________________________
*** CID 509200:  Error handling issues  (CHECKED_RETURN)
/src/util.c: 831 in p11prov_uri_set_label()
825         return uri->object;
826     }
827    
828     void p11prov_uri_set_label(P11PROV_URI *uri, CK_ATTRIBUTE *label)
829     {
830         OPENSSL_free(uri->object.pValue);
>>>     CID 509200:  Error handling issues  (CHECKED_RETURN)
>>>     Calling "p11prov_copy_attr" without checking return value (as is done elsewhere 10 out of 12 times).
831         p11prov_copy_attr(&uri->object, label);
832     }
833    
834     char *p11prov_uri_get_serial(P11PROV_URI *uri)
835     {
836         return uri->serial;

** CID 509199:  Memory - illegal accesses  (USE_AFTER_FREE)
/src/objects.c: 2742 in digest()


________________________________________________________________________________________________________
*** CID 509199:  Memory - illegal accesses  (USE_AFTER_FREE)
/src/objects.c: 2742 in digest()
2736         dgst = NULL;
2737         rv = CKR_OK;
2738    
2739     done:
2740         OPENSSL_free(dgst);
2741         EVP_MD_CTX_free(mdctx);
>>>     CID 509199:  Memory - illegal accesses  (USE_AFTER_FREE)
>>>     Passing freed pointer "md" as an argument to "EVP_MD_free".
2742         EVP_MD_free(md);
2743         return rv;
2744     }
2745    
2746     static CK_RV prep_rsa_find(P11PROV_CTX *ctx, const OSSL_PARAM params[],
2747                                struct pool_find_ctx *findctx)

** CID 509198:  Error handling issues  (CHECKED_RETURN)
/src/util.c: 820 in p11prov_uri_set_id()


________________________________________________________________________________________________________
*** CID 509198:  Error handling issues  (CHECKED_RETURN)
/src/util.c: 820 in p11prov_uri_set_id()
814         return uri->id;
815     }
816    
817     void p11prov_uri_set_id(P11PROV_URI *uri, CK_ATTRIBUTE *id)
818     {
819         OPENSSL_free(uri->id.pValue);
>>>     CID 509198:  Error handling issues  (CHECKED_RETURN)
>>>     Calling "p11prov_copy_attr" without checking return value (as is done elsewhere 10 out of 12 times).
820         p11prov_copy_attr(&uri->id, id);
821     }
822    
823     CK_ATTRIBUTE p11prov_uri_get_label(P11PROV_URI *uri)
824     {
825         return uri->object;

[simo5]

@Jakuje I should have addressed all the changes I agreed on.
Only one comment was unclear to me.

[simo5]

@Jakuje I'll run covscan again one you confirm all the requested changes are ok

[Jakuje]

lgtm

[simo5]

Covscan is happy too, merging.
thanks for the review @Jakuje