Right now, there's no specific way to determine whether a credential
helper or git credential itself supports a given set of capabilities.
It would be helpful to have such a way, so let's let credential helpers
and git credential take an argument, "capability", which has it list the
capabilities and a version number on standard output.
Specifically choose a format that is slightly different from regular
credential output and assume that no capabilities are supported if a
non-zero exit status occurs or the data deviates from the format. It is
common for users to write small shell scripts as the argument to
credential.helper, which will almost never be designed to emit
capabilities. We want callers to gracefully handle this case by
assuming that they are not capable of extended support because that is
almost certainly the case, and specifying the error behavior up front
does this and preserves backwards compatibility in a graceful way.
Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Now that we have full support in Git for the authtype capability, let's
add support to the cache credential helper.
When parsing data, we always set the initial capabilities because we're
the helper, and we need both the initial and helper capabilities to be
set in order to have the helper capabilities take effect.
When emitting data, always emit the supported capability and make sure
we emit items only if we have them and they're supported by the caller.
Since we may no longer have a username or password, be sure to emit
those conditionally as well so we don't segfault on a NULL pointer.
Similarly, when comparing credentials, consider both the password and
credential fields when we're matching passwords.
Adjust the partial credential detection code so that we can store
credentials missing a username or password as long as they have an
authtype and credential.
Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Over HTTP, NTLM and Kerberos require two rounds of authentication on the
client side. It's possible that there are custom authentication schemes
that also implement this same approach. Since these are tricky schemes
to implement and the HTTP library in use may not always handle them
gracefully on all systems, it would be helpful to allow the credential
helper to implement them instead for increased portability and
robustness.
To allow this to happen, add a boolean flag, continue, that indicates
that instead of failing when we get a 401, we should retry another round
of authentication. However, this necessitates some changes in our
current credential code so that we can make this work.
Keep the state[] headers between iterations, but only use them to send
to the helper and only consider the new ones we read from the credential
helper to be valid on subsequent iterations. That avoids us passing
stale data when we finally approve or reject the credential. Similarly,
clear the multistage and wwwauth[] values appropriately so that we
don't pass stale data or think we're trying a multiround response when
we're not. Remove the credential values so that we can actually fill a
second time with new responses.
Limit the number of iterations of reauthentication we do to 3. This
means that if there's a problem, we'll terminate with an error message
instead of retrying indefinitely and not informing the user (and
possibly conducting a DoS on the server).
In our tests, handle creating multiple response output files from our
helper so we can verify that each of the messages sent is correct.
Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Until now, our credential code has mostly deal with usernames and
passwords and we've let libcurl deal with the variant of authentication
to be used. However, now that we have the credential value, the
credential helper can take control of the authentication, so the value
provided might be something that's generated, such as a Digest hash
value.
In such a case, it would be helpful for a credential helper that gets an
erase or store command to be able to keep track of an identifier for the
original secret that went into the computation. Furthermore, some types
of authentication, such as NTLM and Kerberos, actually need two round
trips to authenticate, which will require that the credential helper
keep some state.
In order to allow for these use cases and others, allow storing state in
a field called "state[]". This value is passed back to the credential
helper that created it, which avoids confusion caused by parsing values
from different helpers.
Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Now that we have support for a wide variety of types of authentication,
it's important to indicate to other credential helpers whether they
should store credentials, since not every credential helper may
intuitively understand all possible values of the authtype field. Do so
with a boolean field called "ephemeral", to indicate whether the
credential is expected to be temporary.
For example, in HTTP Digest authentication, the Authorization header
value is based off a nonce. It isn't useful to store this value
for later use because reusing the credential long term will not result
in successful authentication due to the nonce necessarily differing.
An additional case is potentially short-lived credentials, which may
last only a few hours. It similarly wouldn't be helper for other
credential helpers to attempt to provide these much later.
We do still pass the value to "git credential store" or "git credential
erase", since it may be helpful to the original helper to know whether
the operation was successful.
Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
We support the new credential and authtype fields, but we lack a way to
indicate to a credential helper that we'd like them to be used. Without
some sort of indication, the credential helper doesn't know if it should
try to provide us a username and password, or a pre-encoded credential.
For example, the helper might prefer a more restricted Bearer token if
pre-encoded credentials are possible, but might have to fall back to
more general username and password if not.
Let's provide a simple way to indicate whether Git (or, for that matter,
the helper) is capable of understanding the authtype and credential
fields. We send this capability when we generate a request, and the
other side may reply to indicate to us that it does, too.
For now, don't enable sending capabilities for the HTTP code. In a
future commit, we'll introduce appropriate handling for that code,
which requires more in-depth work.
The logic for determining whether a capability is supported may seem
complex, but it is not. At each stage, we emit the capability to the
following stage if all preceding stages have declared it. Thus, if the
caller to git credential fill didn't declare it, then we won't send it
to the helper, and if fill's caller did send but the helper doesn't
understand it, then we won't send it on in the response. If we're an
internal user, then we know about all capabilities and will request
them.
For "git credential approve" and "git credential reject", we set the
helper capability before calling the helper, since we assume that the
input we're getting from the external program comes from a previous call
to "git credential fill", and thus we'll invoke send a capability to the
helper if and only if we got one from the standard input, which is the
correct behavior.
Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
At the moment, our credential code wants to find a username and password
for access, which, for HTTP, it will pass to libcurl to encode and
process. However, many users want to use authentication schemes that
libcurl doesn't support, such as Bearer authentication. In these
schemes, the secret is not a username and password pair, but some sort
of token that meets the production for authentication data in the RFC.
In fact, in general, it's useful to allow our credential helper to have
knowledge about what specifically to put in the protocol header. Thus,
add a field, credential, which contains data that's preencoded to be
suitable for the protocol in question. If we have such data, we need
neither a username nor a password, so make that adjustment as well.
It is in theory possible to reuse the password field for this. However,
if we do so, we must know whether the credential helper supports our new
scheme before sending it data, which necessitates some sort of
capability inquiry, because otherwise an uninformed credential helper
would store our preencoded data as a password, which would fail the next
time we attempted to connect to the remote server. This design is
substantially simpler, and we can hint to the credential helper that we
support this approach with a simple new field instead of needing to
query it first.
Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When Git makes an HTTP request, it can negotiate the type of
authentication to use with the server provided the authentication scheme
is one of a few well-known types (Basic, Digest, NTLM, or Negotiate).
However, some servers wish to use other types of authentication, such as
the Bearer type from OAuth2. Since libcurl doesn't natively support
this type, it isn't possible to use it, and the user is forced to
specify the Authorization header using the http.extraheader setting.
However, storing a plaintext token in the repository configuration is
not very secure, especially if a repository can be shared by multiple
parties. We already have support for many types of secure credential
storage by using credential helpers, so let's teach credential helpers
how to produce credentials for an arbitrary scheme.
If the credential helper specifies an authtype field, then it specifies
an authentication scheme (e.g., Bearer) and the password field specifies
the raw authentication token, with any encoding already specified. We
reuse the password field for this because some credential helpers store
the metadata without encryption even though the password is encrypted,
and we'd like to avoid insecure storage if an older version of the
credential helper gets ahold of the data.
The username is not used in this case, but it is still preserved for the
purpose of finding the right credential if the user has multiple
accounts.
If the authtype field is not specified, then the password behaves as
normal and it is passed along with the username to libcurl.
Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Test that credential helpers do not erase a password distinct from the
input. Such calls can happen when multiple credential helpers are
configured.
Fixes for credential-cache and credential-store.
Signed-off-by: M Hickford <mirth.hickford@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Git authentication with OAuth access token is supported by every popular
Git host including GitHub, GitLab and BitBucket [1][2][3]. Credential
helpers Git Credential Manager (GCM) and git-credential-oauth generate
OAuth credentials [4][5]. Following RFC 6749, the application prints a
link for the user to authorize access in browser. A loopback redirect
communicates the response including access token to the application.
For security, RFC 6749 recommends that OAuth response also includes
expiry date and refresh token [6]. After expiry, applications can use
the refresh token to generate a new access token without user
reauthorization in browser. GitLab and BitBucket set the expiry at two
hours [2][3]. (GitHub doesn't populate expiry or refresh token.)
However the Git credential protocol has no attribute to store the OAuth
refresh token (unrecognised attributes are silently discarded). This
means that the user has to regularly reauthorize the helper in browser.
On a browserless system, this is particularly intrusive, requiring a
second device.
Introduce a new attribute oauth_refresh_token. This is especially
useful when a storage helper and a read-only OAuth helper are configured
together. Recall that `credential fill` calls each helper until it has a
non-expired password.
```
[credential]
helper = storage # eg. cache or osxkeychain
helper = oauth
```
The OAuth helper can use the stored refresh token forwarded by
`credential fill` to generate a fresh access token without opening the
browser. See
https://github.com/hickford/git-credential-oauth/pull/3/files
for an implementation tested with this patch.
Add support for the new attribute to credential-cache. Eventually, I
hope to see support in other popular storage helpers.
Alternatives considered: ask helpers to store all unrecognised
attributes. This seems excessively complex for no obvious gain.
Helpers would also need extra information to distinguish between
confidential and non-confidential attributes.
Workarounds: GCM abuses the helper get/store/erase contract to store the
refresh token during credential *get* as the password for a fictitious
host [7] (I wrote this hack). This workaround is only feasible for a
monolithic helper with its own storage.
[1] https://github.blog/2012-09-21-easier-builds-and-deployments-using-git-over-https-and-oauth/
[2] https://docs.gitlab.com/ee/api/oauth2.html#access-git-over-https-with-access-token
[3] https://support.atlassian.com/bitbucket-cloud/docs/use-oauth-on-bitbucket-cloud/#Cloning-a-repository-with-an-access-token
[4] https://github.com/GitCredentialManager/git-credential-manager
[5] https://github.com/hickford/git-credential-oauth
[6] https://datatracker.ietf.org/doc/html/rfc6749#section-5.1
[7] 66b94e489a/src/shared/GitLab/GitLabHostProvider.cs (L207)
Signed-off-by: M Hickford <mirth.hickford@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Allow information carried on the WWW-AUthenticate header to be
passed to the credential helpers.
* mc/credential-helper-www-authenticate:
credential: add WWW-Authenticate header to cred requests
http: read HTTP WWW-Authenticate response headers
t5563: add tests for basic and anoymous HTTP access
Read and store the HTTP WWW-Authenticate response headers made for
a particular request.
This will allow us to pass important authentication challenge
information to credential helpers or others that would otherwise have
been lost.
libcurl only provides us with the ability to read all headers recieved
for a particular request, including any intermediate redirect requests
or proxies. The lines returned by libcurl include HTTP status lines
delinating any intermediate requests such as "HTTP/1.1 200". We use
these lines to reset the strvec of WWW-Authenticate header values as
we encounter them in order to only capture the final response headers.
The collection of all header values matching the WWW-Authenticate
header is complicated by the fact that it is legal for header fields to
be continued over multiple lines, but libcurl only gives us each
physical line a time, not each logical header. This line folding feature
is deprecated in RFC 7230 [1] but older servers may still emit them, so
we need to handle them.
In the future [2] we may be able to leverage functions to read headers
from libcurl itself, but as of today we must do this ourselves.
[1] https://www.rfc-editor.org/rfc/rfc7230#section-3.2
[2] https://daniel.haxx.se/blog/2022/03/22/a-headers-api-for-libcurl/
Signed-off-by: Matthew John Cheetham <mjcheetham@outlook.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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>
Move *_INIT macros I'll use in a subsequent commits to designated
initializers. This isn't required for those follow-up changes, but
since next commits will change things in this area, let's use the
modern pattern over the old one while we're at it.
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Since the beginning in 118250728e (credential: apply helper config,
2011-12-10), the declaration for that function used a different order
than the implementation.
All callers use the same order than the implementation, so update
the declaration in credential.h to match.
Reviewed-by: Jeff King <peff@peff.net>
Signed-off-by: Carlo Marcelo Arenas Belón <carenas@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
c44088ecc4 (credential: treat URL without scheme as invalid, 2020-04-18)
changes the implementation for this function to return -1 if protocol is
missing.
Update blurb to match implementation.
Reviewed-by: Jeff King <peff@peff.net>
Signed-off-by: Carlo Marcelo Arenas Belón <carenas@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The credential protocol can't represent newlines in values, but URLs can
embed percent-encoded newlines in various components. A previous commit
taught the low-level writing routines to die() when encountering this,
but we can be a little friendlier to the user by detecting them earlier
and handling them gracefully.
This patch teaches credential_from_url() to notice such components,
issue a warning, and blank the credential (which will generally result
in prompting the user for a username and password). We blank the whole
credential in this case. Another option would be to blank only the
invalid component. However, we're probably better off not feeding a
partially-parsed URL result to a credential helper. We don't know how a
given helper would handle it, so we're better off to err on the side of
matching nothing rather than something unexpected.
The die() call in credential_write() is _probably_ impossible to reach
after this patch. Values should end up in credential structs only by URL
parsing (which is covered here), or by reading credential protocol input
(which by definition cannot read a newline into a value). But we should
definitely keep the low-level check, as it's our final and most accurate
line of defense against protocol injection attacks. Arguably it could
become a BUG(), but it probably doesn't matter much either way.
Note that the public interface of credential_from_url() grows a little
more than we need here. We'll use the extra flexibility in a future
patch to help fsck catch these cases.
A configuration element used for credential subsystem can now use
wildcard pattern to specify for which set of URLs the entry
applies.
* bc/wildcard-credential:
credential: allow wildcard patterns when matching config
credential: use the last matching username in the config
t0300: add tests for some additional cases
t1300: add test for urlmatch with multiple wildcards
mailmap: add an additional email address for brian m. carlson
Everywhere else in the codebase, we use the rule that the last matching
configuration option is the one that takes effect. This is helpful
because it allows more specific configuration settings (e.g., per-repo
configuration) to override less specific settings (e.g., per-user
configuration).
However, in the credential code, we didn't honor this setting, and
instead picked the first setting we had, and stuck with it. This was
likely to ensure we picked the value from the URL, which we want to
honor over the configuration.
It's possible to do both, though, so let's check if the value is the one
we've gotten over our protocol connection, which if present will have
come from the URL, and keep it if so. Otherwise, let's overwrite the
value with the latest version we've got from the configuration, so we
keep the last configuration value.
Signed-off-by: brian m. carlson <bk2204@github.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The details of how credential helpers can be called or implemented were
originally covered in Documentation/technical/. Those are topics that
end users might care about (and we even referenced them in the
credentials manpage), but those docs typically don't ship as part of the
end user documentation, making them less useful.
This situation got slightly worse recently in f3b9055624 (credential:
move doc to credential.h, 2019-11-17), where we moved them into the C
header file, making them even harder to find.
So let's move put this information into the gitcredentials(7)
documentation, which is meant to describe the overall concepts of our
credential handling. This was already pointing to the API docs for these
concepts, so we can just include it inline instead.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Move the documentation from Documentation/technical/api-credentials.txt
to credential.h as it's easier for the developers to find the usage
information beside the code instead of looking for it in another doc file.
Documentation/technical/api-credentials.txt is removed because the
information it has is now redundant and it'll be hard to keep it up to
date and synchronized with the documentation in the header file.
Documentation/git-credential.txt and Documentation/gitcredentials.txt now link
to credential.h instead of Documentation/technical/api-credentials.txt for
details about the credetials API.
Signed-off-by: Heba Waly <heba.waly@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When we are trying to fill a credential, we loop over the
set of defined credential-helpers, then fall back to running
askpass, and then finally prompt on the terminal. Helpers
which cannot find a credential are free to tell us nothing,
but they cannot currently ask us to stop prompting.
This patch lets them provide a "quit" attribute, which asks
us to stop the process entirely (avoiding running more
helpers, as well as the askpass/terminal prompt).
This has a few possible uses:
1. A helper which prompts the user itself (e.g., in a
dialog) can provide a "cancel" button to the user to
stop further prompts.
2. Some helpers may know that prompting cannot possibly
work. For example, if their role is to broker a ticket
from an external auth system and that auth system
cannot be contacted, there is no point in continuing
(we need a ticket to authenticate, and the user cannot
provide one by typing it in).
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
Instead of outputing only the username and password, print all the
attributes, even those that already appeared in the input.
This is closer to what the C API does, and allows one to take the exact
output of "git credential fill" as input to "git credential approve" or
"git credential reject".
Signed-off-by: Junio C Hamano <gitster@pobox.com>
When parsing a URL into a credential struct, we carefully
record each part of the URL, including the path on the
remote host, and use the result as part of the credential
context.
This had two practical implications:
1. Credential helpers which store a credential for later
access are likely to use the "path" portion as part of
the storage key. That means that a request to
https://example.com/foo.git
would not use the same credential that was stored in an
earlier request for:
https://example.com/bar.git
2. The prompt shown to the user includes all relevant
context, including the path.
In most cases, however, users will have a single password
per host. The behavior in (1) will be inconvenient, and the
prompt in (2) will be overly long.
This patch introduces a config option to toggle the
relevance of http paths. When turned on, we use the path as
before. When turned off, we drop the path component from the
context: helpers don't see it, and it does not appear in the
prompt.
This is nothing you couldn't do with a clever credential
helper at the start of your stack, like:
[credential "http://"]
helper = "!f() { grep -v ^path= ; }; f"
helper = your_real_helper
But doing this:
[credential]
useHttpPath = false
is way easier and more readable. Furthermore, since most
users will want the "off" behavior, that is the new default.
Users who want it "on" can set the variable (either for all
credentials, or just for a subset using
credential.*.useHttpPath).
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The functionality for credential storage helpers is already
there; we just need to give the users a way to turn it on.
This patch provides a "credential.helper" configuration
variable which allows the user to provide one or more helper
strings.
Rather than simply matching credential.helper, we will also
compare URLs in subsection headings to the current context.
This means you can apply configuration to a subset of
credentials. For example:
[credential "https://example.com"]
helper = foo
would match a request for "https://example.com/foo.git", but
not one for "https://kernel.org/foo.git".
This is overkill for the "helper" variable, since users are
unlikely to want different helpers for different sites (and
since helpers run arbitrary code, they could do the matching
themselves anyway).
However, future patches will add new config variables where
this extra feature will be more useful.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
All of the components of a credential struct can be found in
a URL. For example, the URL:
http://foo:bar@example.com/repo.git
contains:
protocol=http
host=example.com
path=repo.git
username=foo
password=bar
We want to be able to turn URLs into broken-down credential
structs so that we know two things:
1. Which parts of the username/password we still need
2. What the context of the request is (for prompting or
as a key for storing credentials).
This code is based on http_auth_init in http.c, but needed a
few modifications in order to get all of the components that
the credential object is interested in.
Once the http code is switched over to the credential API,
then http_auth_init can just go away.
Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
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>
brian m. carlson
M Hickford
Junio C Hamano
Matthew John Cheetham
Ævar Arnfjörð Bjarmason
Carlo Marcelo Arenas Belón
Jeff King
brian m. carlson
Heba Waly
Matthieu Moy