credential: new attribute password_expiry_utc

Some passwords have an expiry date known at generation. This may be
years away for a personal access token or hours for an OAuth access
token.

When multiple credential helpers are configured, `credential fill` tries
each helper in turn until it has a username and password, returning
early. If Git authentication succeeds, `credential approve`
stores the successful credential in all helpers. If authentication
fails, `credential reject` erases matching credentials in all helpers.
Helpers implement corresponding operations: get, store, erase.

The credential protocol has no expiry attribute, so helpers cannot
store expiry information. Even if a helper returned an improvised
expiry attribute, git credential discards unrecognised attributes
between operations and between helpers.

This is a particular issue when a storage helper and a
credential-generating helper are configured together:

	[credential]
		helper = storage  # eg. cache or osxkeychain
		helper = generate  # eg. oauth

`credential approve` stores the generated credential in both helpers
without expiry information. Later `credential fill` may return an
expired credential from storage. There is no workaround, no matter how
clever the second helper. The user sees authentication fail (a retry
will succeed).

Introduce a password expiry attribute. In `credential fill`, ignore
expired passwords and continue to query subsequent helpers.

In the example above, `credential fill` ignores the expired password
and a fresh credential is generated. If authentication succeeds,
`credential approve` replaces the expired password in storage.
If authentication fails, the expired credential is erased by
`credential reject`. It is unnecessary but harmless for storage
helpers to self prune expired credentials.

Add support for the new attribute to credential-cache.
Eventually, I hope to see support in other popular storage helpers.

Example usage in a credential-generating helper
https://github.com/hickford/git-credential-oauth/pull/16

Signed-off-by: M Hickford <mirth.hickford@gmail.com>
Reviewed-by: Calvin Wan <calvinwan@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 94 insertions, 0 deletions

diff --git a/t/t0300-credentials.sh b/t/t0300-credentials.sh
index 3485c0534e..c66d91e82d 100755
--- a/t/t0300-credentials.sh
+++ b/t/t0300-credentials.sh
@@ -35,6 +35,16 @@ test_expect_success 'setup helper scripts' '
 	test -z "$pass" || echo password=$pass
 	EOF
 
+	write_script git-credential-verbatim-with-expiry <<-\EOF &&
+	user=$1; shift
+	pass=$1; shift
+	pexpiry=$1; shift
+	. ./dump
+	test -z "$user" || echo username=$user
+	test -z "$pass" || echo password=$pass
+	test -z "$pexpiry" || echo password_expiry_utc=$pexpiry
+	EOF
+
 	PATH="$PWD:$PATH"
 '
 
@@ -109,6 +119,43 @@ test_expect_success 'credential_fill continues through partial response' '
 	EOF
 '
 
+test_expect_success 'credential_fill populates password_expiry_utc' '
+	check fill "verbatim-with-expiry one two 9999999999" <<-\EOF
+	protocol=http
+	host=example.com
+	--
+	protocol=http
+	host=example.com
+	username=one
+	password=two
+	password_expiry_utc=9999999999
+	--
+	verbatim-with-expiry: get
+	verbatim-with-expiry: protocol=http
+	verbatim-with-expiry: host=example.com
+	EOF
+'
+
+test_expect_success 'credential_fill ignores expired password' '
+	check fill "verbatim-with-expiry one two 5" "verbatim three four" <<-\EOF
+	protocol=http
+	host=example.com
+	--
+	protocol=http
+	host=example.com
+	username=three
+	password=four
+	--
+	verbatim-with-expiry: get
+	verbatim-with-expiry: protocol=http
+	verbatim-with-expiry: host=example.com
+	verbatim: get
+	verbatim: protocol=http
+	verbatim: host=example.com
+	verbatim: username=one
+	EOF
+'
+
 test_expect_success 'credential_fill passes along metadata' '
 	check fill "verbatim one two" <<-\EOF
 	protocol=ftp
@@ -149,6 +196,24 @@ test_expect_success 'credential_approve calls all helpers' '
 	EOF
 '
 
+test_expect_success 'credential_approve stores password expiry' '
+	check approve useless <<-\EOF
+	protocol=http
+	host=example.com
+	username=foo
+	password=bar
+	password_expiry_utc=9999999999
+	--
+	--
+	useless: store
+	useless: protocol=http
+	useless: host=example.com
+	useless: username=foo
+	useless: password=bar
+	useless: password_expiry_utc=9999999999
+	EOF
+'
+
 test_expect_success 'do not bother storing password-less credential' '
 	check approve useless <<-\EOF
 	protocol=http
@@ -159,6 +224,17 @@ test_expect_success 'do not bother storing password-less credential' '
 	EOF
 '
 
+test_expect_success 'credential_approve does not store expired password' '
+	check approve useless <<-\EOF
+	protocol=http
+	host=example.com
+	username=foo
+	password=bar
+	password_expiry_utc=5
+	--
+	--
+	EOF
+'
 
 test_expect_success 'credential_reject calls all helpers' '
 	check reject useless "verbatim one two" <<-\EOF
@@ -181,6 +257,24 @@ test_expect_success 'credential_reject calls all helpers' '
 	EOF
 '
 
+test_expect_success 'credential_reject erases credential regardless of expiry' '
+	check reject useless <<-\EOF
+	protocol=http
+	host=example.com
+	username=foo
+	password=bar
+	password_expiry_utc=5
+	--
+	--
+	useless: erase
+	useless: protocol=http
+	useless: host=example.com
+	useless: username=foo
+	useless: password=bar
+	useless: password_expiry_utc=5
+	EOF
+'
+
 test_expect_success 'usernames can be preserved' '
 	check fill "verbatim \"\" three" <<-\EOF
 	protocol=http