introduce credentials API

There are a few places in git that need to get a username
and password credential from the user; the most notable one
is HTTP authentication for smart-http pushing.

Right now the only choices for providing credentials are to
put them plaintext into your ~/.netrc, or to have git prompt
you (either on the terminal or via an askpass program). The
former is not very secure, and the latter is not very
convenient.

Unfortunately, there is no "always best" solution for
password management. The details will depend on the tradeoff
you want between security and convenience, as well as how
git can integrate with other security systems (e.g., many
operating systems provide a keychain or password wallet for
single sign-on).

This patch provides an abstract notion of credentials as a
data item, and provides three basic operations:

  - fill (i.e., acquire from external storage or from the
    user)

  - approve (mark a credential as "working" for further
    storage)

  - reject (mark a credential as "not working", so it can
    be removed from storage)

These operations can be backed by external helper processes
that interact with system- or user-specific secure storage.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

2 files changed, 228 insertions, 0 deletions

diff --git a/t/lib-credential.sh b/t/lib-credential.sh
new file mode 100755
index 0000000000..54ae1f484c
--- /dev/null
+++ b/t/lib-credential.sh
@@ -0,0 +1,33 @@
+#!/bin/sh
+
+# Try a set of credential helpers; the expected stdin,
+# stdout and stderr should be provided on stdin,
+# separated by "--".
+check() {
+	read_chunk >stdin &&
+	read_chunk >expect-stdout &&
+	read_chunk >expect-stderr &&
+	test-credential "$@" <stdin >stdout 2>stderr &&
+	test_cmp expect-stdout stdout &&
+	test_cmp expect-stderr stderr
+}
+
+read_chunk() {
+	while read line; do
+		case "$line" in
+		--) break ;;
+		*) echo "$line" ;;
+		esac
+	done
+}
+
+
+cat >askpass <<\EOF
+#!/bin/sh
+echo >&2 askpass: $*
+what=`echo $1 | cut -d" " -f1 | tr A-Z a-z | tr -cd a-z`
+echo "askpass-$what"
+EOF
+chmod +x askpass
+GIT_ASKPASS="$PWD/askpass"
+export GIT_ASKPASS
diff --git a/t/t0300-credentials.sh b/t/t0300-credentials.sh
new file mode 100755
index 0000000000..81a455f4c3
--- /dev/null
+++ b/t/t0300-credentials.sh
@@ -0,0 +1,195 @@
+#!/bin/sh
+
+test_description='basic credential helper tests'
+. ./test-lib.sh
+. "$TEST_DIRECTORY"/lib-credential.sh
+
+test_expect_success 'setup helper scripts' '
+	cat >dump <<-\EOF &&
+	whoami=`echo $0 | sed s/.*git-credential-//`
+	echo >&2 "$whoami: $*"
+	while IFS== read key value; do
+		echo >&2 "$whoami: $key=$value"
+		eval "$key=$value"
+	done
+	EOF
+
+	cat >git-credential-useless <<-\EOF &&
+	#!/bin/sh
+	. ./dump
+	exit 0
+	EOF
+	chmod +x git-credential-useless &&
+
+	cat >git-credential-verbatim <<-\EOF &&
+	#!/bin/sh
+	user=$1; shift
+	pass=$1; shift
+	. ./dump
+	test -z "$user" || echo username=$user
+	test -z "$pass" || echo password=$pass
+	EOF
+	chmod +x git-credential-verbatim &&
+
+	PATH="$PWD:$PATH"
+'
+
+test_expect_success 'credential_fill invokes helper' '
+	check fill "verbatim foo bar" <<-\EOF
+	--
+	username=foo
+	password=bar
+	--
+	verbatim: get
+	EOF
+'
+
+test_expect_success 'credential_fill invokes multiple helpers' '
+	check fill useless "verbatim foo bar" <<-\EOF
+	--
+	username=foo
+	password=bar
+	--
+	useless: get
+	verbatim: get
+	EOF
+'
+
+test_expect_success 'credential_fill stops when we get a full response' '
+	check fill "verbatim one two" "verbatim three four" <<-\EOF
+	--
+	username=one
+	password=two
+	--
+	verbatim: get
+	EOF
+'
+
+test_expect_success 'credential_fill continues through partial response' '
+	check fill "verbatim one \"\"" "verbatim two three" <<-\EOF
+	--
+	username=two
+	password=three
+	--
+	verbatim: get
+	verbatim: get
+	verbatim: username=one
+	EOF
+'
+
+test_expect_success 'credential_fill passes along metadata' '
+	check fill "verbatim one two" <<-\EOF
+	protocol=ftp
+	host=example.com
+	path=foo.git
+	--
+	username=one
+	password=two
+	--
+	verbatim: get
+	verbatim: protocol=ftp
+	verbatim: host=example.com
+	verbatim: path=foo.git
+	EOF
+'
+
+test_expect_success 'credential_approve calls all helpers' '
+	check approve useless "verbatim one two" <<-\EOF
+	username=foo
+	password=bar
+	--
+	--
+	useless: store
+	useless: username=foo
+	useless: password=bar
+	verbatim: store
+	verbatim: username=foo
+	verbatim: password=bar
+	EOF
+'
+
+test_expect_success 'do not bother storing password-less credential' '
+	check approve useless <<-\EOF
+	username=foo
+	--
+	--
+	EOF
+'
+
+
+test_expect_success 'credential_reject calls all helpers' '
+	check reject useless "verbatim one two" <<-\EOF
+	username=foo
+	password=bar
+	--
+	--
+	useless: erase
+	useless: username=foo
+	useless: password=bar
+	verbatim: erase
+	verbatim: username=foo
+	verbatim: password=bar
+	EOF
+'
+
+test_expect_success 'usernames can be preserved' '
+	check fill "verbatim \"\" three" <<-\EOF
+	username=one
+	--
+	username=one
+	password=three
+	--
+	verbatim: get
+	verbatim: username=one
+	EOF
+'
+
+test_expect_success 'usernames can be overridden' '
+	check fill "verbatim two three" <<-\EOF
+	username=one
+	--
+	username=two
+	password=three
+	--
+	verbatim: get
+	verbatim: username=one
+	EOF
+'
+
+test_expect_success 'do not bother completing already-full credential' '
+	check fill "verbatim three four" <<-\EOF
+	username=one
+	password=two
+	--
+	username=one
+	password=two
+	--
+	EOF
+'
+
+# We can't test the basic terminal password prompt here because
+# getpass() tries too hard to find the real terminal. But if our
+# askpass helper is run, we know the internal getpass is working.
+test_expect_success 'empty helper list falls back to internal getpass' '
+	check fill <<-\EOF
+	--
+	username=askpass-username
+	password=askpass-password
+	--
+	askpass: Username:
+	askpass: Password:
+	EOF
+'
+
+test_expect_success 'internal getpass does not ask for known username' '
+	check fill <<-\EOF
+	username=foo
+	--
+	username=foo
+	password=askpass-password
+	--
+	askpass: Password:
+	EOF
+'
+
+test_done