More cleanly contextualize secrets

[jglick]

In order to generate a proper JWT

conjur-credentials-plugin/src/main/java/org/conjur/jenkins/jwtauth/impl/JwtToken.java

Lines 131 to 133 in 86da1cc

	if (contextObject instanceof Run) {
	Run run = (Run) contextObject;
	jwtToken.claim.put("jenkins_build_number", run.getNumber());

this plugin needs to do some tricks.

conjur-credentials-plugin/src/main/java/org/conjur/jenkins/credentials/ConjurCredentialProvider.java

Lines 56 to 57 in 86da1cc

	public <C extends Credentials> List<C> getCredentials(@Nonnull Class<C> type,
	@Nonnull Item item,

almost has enough information, but not quite; CredentialsProvider.findCredentialById passes a Job but not a Run to an implementation.

conjur-credentials-plugin/src/main/java/org/conjur/jenkins/conjursecrets/ConjurSecretCredentialsBinding.java

Lines 61 to 62 in 86da1cc

	ConjurSecretCredentials conjurSecretCredential = getCredentials(build);
	conjurSecretCredential.setContext(build);

abuses the credentials-binding plugin for this purpose, but that will not work in all cases. I am hoping jenkinsci/credentials-plugin#293 will allow this to be solved cleanly.