[WIP]Support podman image sign

Generate a signature claim for an image using user keyring (--sign-by). The signature file will be stored in simple json format under the default or the given directory (--directory or yaml file in /etc/containers/registries.d/).

Signed-off-by: Qi Wang <qiwan@redhat.com>

1 files changed, 52 insertions, 0 deletions

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+% podman-image-sign(1)
+
+# NAME
+podman-image-sign- Create a signature for an image
+
+# SYNOPSIS
+**podman image sign**
+[**-h**|**--help**]
+[**-d**, **--directory**]
+[**--sign-by**]
+[ IMAGE... ]
+
+# DESCRIPTION
+**podmain image sign** will create a local signature for one or more local images that have
+been pulled from a registry. The signature will be written to a directory
+derived from the registry configuration files in /etc/containers/registries.d. By default, the signature will be written into /var/lib/containers/sigstore directory.
+
+# OPTIONS
+**-h** **--help**
+  Print usage statement.
+
+**-d** **--directory**
+  Store the signatures in the specified directory.  Default: /var/lib/containers/sigstore
+
+**--sign-by**
+  Override the default identity of the signature.
+
+# EXAMPLES
+Sign the busybox image with the identify of foo@bar.com with a user's keyring and save the signature in /tmp/signatures/.
+
+   sudo podman image sign --sign-by foo@bar.com -d /tmp/signatures transport://privateregistry.example.com/foobar
+
+# RELATED CONFIGURATION
+
+The write (and read) location for signatures is defined in YAML-based
+configuration files in /etc/containers/registries.d/.  When you sign
+an image, podman will use those configuration files to determine
+where to write the signature based on the the name of the originating
+registry or a default storage value unless overriden with the -d
+option. For example, consider the following configuration file.
+
+docker:
+  privateregistry.example.com:
+    sigstore: file:///var/lib/containers/sigstore
+
+When signing an image preceeded with the registry name 'privateregistry.example.com',
+the signature will be written into subdirectories of
+/var/lib/containers/sigstore/privateregistry.example.com. The use of 'sigstore' also means
+the signature will be 'read' from that same location on a pull-related function.
+
+# HISTORY
+November 2018, Originally compiled by Qi Wang (qiwan at redhat dot com)