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Update GCP auth BE docs (#5753)
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Documented changes from hashicorp/vault-plugin-auth-gcp#55
* Deprecating `project_id` for `bound_projects` and making it optional
* Deprecating `google_certs_endpoint` (unused)
* Adding group aliases 

Also, some general reformatting
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emilymye authored and kalafut committed Dec 10, 2018
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30 changes: 16 additions & 14 deletions website/source/api/auth/gcp/index.html.md
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Expand Up @@ -45,11 +45,6 @@ to confirm signed JWTs passed in during login.

The project must have the `iam.googleapis.com` API [enabled](https://console.cloud.google.com/flows/enableapi?apiid=iam.googleapis.com).

- `google_certs_endpoint` `(string:
"https://www.googleapis.com/oauth2/v3/certs")`: The Google OAuth2 endpoint
from which to obtain public certificates. This is used for testing and should
generally not be set by end users.

### Sample Payload

```json
Expand Down Expand Up @@ -133,9 +128,6 @@ entities attempting to login.
correspond to specific roles and will be rejected otherwise. Please see below
for more information.

- `project_id` `(string: <required>)` - The GCP project ID. Only entities belonging to this
project can authenticate with this role.

- `ttl` `(string: "")` - The TTL period of tokens issued using this role. This
can be specified as an integer number of seconds or as a duration value like
"5m".
Expand All @@ -153,12 +145,21 @@ entities attempting to login.
- `policies` `(array: [default])` - The list of policies to be set on tokens
issued using this role.

- `bound_service_accounts` `(array: <required for iam>)` - A comma-separated
list of service account emails or IDs that login is restricted to. If set to
`*`, all service accounts are allowed (role will still be bound by project).
Will be inferred from service account used to issue metadata token for GCE
instances.

- `bound_service_accounts` `(array: <required for iam>)` - An array of
service account emails or IDs that login is restricted to,
either directly or through an associated instance. If set to
`*`, all service accounts are allowed (you can bind this further using
`bound_projects`.)

- `bound_projects` `(array: [])` - An array of GCP project IDs. Only entities
belonging to this project can authenticate under the role.

- `add_group_aliases` `(bool: false)` - If true, any auth token
generated under this token will have associated group aliases, namely
`project-$PROJECT_ID`, `folder-$PROJECT_ID`, and `organization-$ORG_ID`
for the entities project and all its folder or organization ancestors. This
requires Vault to have IAM permission `resourcemanager.projects.get`.

#### `iam`-only Parameters

The following parameters are only valid when the role is of type `"iam"`:
Expand Down Expand Up @@ -486,6 +487,7 @@ $ curl \
"prod"
],
"metadata": {
"project_id": "my-project",
"role": "my-role",
"service_account_email": "[email protected]",
"service_account_id": "111111111111111111111"
Expand Down
196 changes: 129 additions & 67 deletions website/source/docs/auth/gcp.html.md
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Expand Up @@ -10,51 +10,105 @@ description: |-

# Google Cloud Auth Method

The `gcp` auth method allows authentication against Vault using Google
credentials. It treats Google Cloud Platform (GCP) as a Trusted Third Party and
expects a [JSON Web Token][jwt] (JWT) signed by Google credentials from the
authenticating entity. This token can be generated through different GCP APIs
depending on the type of entity.
The `gcp` auth method allows Google Cloud Platform (GCP) entities to
authenticate to Vault. Vault treats GCP as a Trusted Third Party and
verifies authenticating entities against GCP APIs. This backend allows
for authentication of:

* IAM service accounts
* Google Compute Engine (GCE) instances

**NOTE**: This backend focuses on identities specific to Google Cloud and
does not support authenticating Google users (i.e. `type: "authorized_user"`)
or OAuth against Google

This plugin is developed in a separate GitHub repository at
[`hashicorp/vault-plugin-auth-gcp`](https://github.com/hashicorp/vault-plugin-auth-gcp),
but is automatically bundled in Vault releases. Please file all feature
requests, bugs, and pull requests specific to the GCP plugin under that
repository.

## Authentication
## Quick Start

To authenticate, you will need two things:

### Via the CLI
1. Proof-of-identity:
* Service Account: A signed [JSON Web Token][jwt] (JWT), or GCP credentials
with permissions to sign a JWT (see [`signJwt`][signjwt-method] IAM API
method) for this service account
* Access to a metadata server for a GCE instance
1. Name of a `role`, a binding of Vault policies and authZ
restrictions preconfigured for the GCP auth backend that
an entity authenticates under. Roles are either type `iam`, which
supports either type of entity, or `gce`, which support only GCE instances.

### Via CLI

The default path is `/gcp`. If this auth method was enabled at a different
path, specify `-path=/my-path` in the CLI.
path, specify `-path=/my-path` in the CLI.
The backend takes a signed [JSON Web Token][jwt] (JWT) as proof-of-identity.

#### Generate `iam` JWT and Login

Because the process to sign a service account JWT can be tedious, Vault includes
a CLI helper that handles obtaining a properly-formatted and signed JWT on your
client before sending an actual request to the Vault server. This process
**only applies to `iam`-type roles!** For GCE instances, the JWT is
automatically generated by Google and exposed as metadata.

```text
$ vault login -method=gcp \
role="my-role" \
jwt="eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9..."
service_account="[email protected]"
project="my-project" \
jwt_exp="15m" \
credentials=@path/to/signer/credentials.json \
```

In this example, the "role" is the name of a configured role. The "jwt" is a
self-signed or Google-signed JWT token obtained using the
[`signJwt`][signjwt-method] API call.
Note that `credentials` must have signJwt permissions on `service_account`.

*Optional Fields*:
* `credentials` can be omitted to default to Application Default Credentials.
* `service_account` or `project` can be omitted and Vault will attempt
to default to values in `credentials`. However, Vault will return an
error if the `credentials` are not a valid service account key file.

For more details on each field, please run `vault auth help gcp`.

#### Login With Existing JWT

If you already have an existing service account JWT that you generated
from the API or by yourself, you can run the following command to
login.

Because the process to sign a service account JWT can be tedious, Vault includes
a CLI helper to generate the JWT token given the service account and parameters.
This process **only applies to `iam`-type roles!**

```text
$ vault login -method=gcp \
role="my-role" \
jwt_exp="15m" \
credentials=@path/to/credentials.json \
project="my-project" \
service_account="[email protected]"
$ vault write -field=token auth/gcp/login role="my-role" jwt="eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9..."
```

This signs a properly formatted service account JWT and authenticates to Vault
directly. For details on each field, please run `vault auth help gcp`.
#### Obtaining `gce` JWT (Metadata)

GCE tokens are obtained from a GCE instance's own metadata server endpoint,
`service-accounts/default/identity`.

**You must run these example commands from the GCE instance.**.

```text
ROLE="my-gce-role"
SERVICE_ACCOUNT="default"
curl \
--header "Metadata-Flavor: Google" \
--get \
--data-urlencode "audience=http://vault/${ROLE}" \
--data-urlencode "format=full" \
"http://metadata/computeMetadata/v1/instance/service-accounts/${SERVICE_ACCOUNT}/identity"
```

Since instances currently only support one service account, you can use
`default` as we do to refer to the associated service account. You can also
use the actual service account email or ID.

### Via the API

```text
Expand All @@ -64,28 +118,7 @@ $ curl \
http://127.0.0.1:8200/v1/auth/gcp/login
```

The response will be in JSON. For example:

```javascript
{
"auth": {
"client_token": "f33f8c72-924e-11f8-cb43-ac59d697597c",
"accessor": "0e9e354a-520f-df04-6867-ee81cae3d42d",
"policies": [
"default",
"dev",
"prod"
],
"metadata": {
"role": "my-role",
"service_account_email": "[email protected]",
"service_account_id": "111111111111111111111"
},
"lease_duration": 2764800,
"renewable": true
}
}
```
See [API docs][api-docs] for expected response.

## Configuration

Expand Down Expand Up @@ -117,7 +150,6 @@ management tool.
```text
$ vault write auth/gcp/role/my-iam-role \
type="iam" \
project_id="my-project" \
policies="dev,prod" \
bound_service_accounts="[email protected]"
```
Expand All @@ -127,8 +159,8 @@ management tool.
```text
$ vault write auth/gcp/role/my-gce-role \
type="gce" \
project_id="my-project" \
policies="dev,prod" \
bound_projects="my-project1,my-project2" \
bound_zones="us-east1-b" \
bound_labels="foo:bar,zip:zap"
```
Expand Down Expand Up @@ -161,14 +193,44 @@ minimum scope(s):
https://www.googleapis.com/auth/cloud-platform
```

## Workflow
### Vault Identity Features

This section describes features related to Vault's
[Identity](/docs/secrets/identity/index.html)
system. Since the Identity system was released after the initial GCP auth
backend plugin was released, this will generally cover features
we have added in newer releases of the plugin.

#### Group Aliases

Roles now have a `add_group_aliases` boolean parameter that adds
[Group Aliases][identity-group-aliases] to the auth response. For example,
for a project `$PROJECT_ID`, in subfolder `$SUBFOLDER_ID`,
in folder `$FOLDER_ID`, in organization `$ORG_ID`, the following group aliases
will be added:

```javascript
[
"project-$PROJECT_ID",
"folder-$SUBFOLDER_ID",
"folder-$FOLDER_ID",
"organization-$ORG_ID"
]
```

Note this is opt-in as it requires a project-level or organizational-level
Google IAM permission `resourcemanager.projects.get`.

## Appendixes

### Implementation Details and Workflow

This section describes the implementation details for how Vault communicates
with Google Cloud to authenticate and authorize JWT tokens. This information is
provided for those who are curious, but these implementation details are not
provided for those who are curious, but these details are not
required knowledge for using the auth method.

### IAM Login
#### IAM Login

IAM login applies only to roles of type `iam`. The Vault authentication workflow
for IAM service accounts looks like this:
Expand All @@ -189,7 +251,7 @@ for IAM service accounts looks like this:
4. Vault authorizes the confirmed service account against the given role. If
that is successful, a Vault token with the proper policies is returned.

### GCE Login
#### GCE Login

GCE login only applies to roles of type `gce` and **must be completed on an
instance running in GCE**. These steps will not work from your local laptop or
Expand All @@ -210,30 +272,27 @@ another cloud provider.
the instance matches the bound zones, regions, or instance groups. If that is
successful, a Vault token with the proper policies is returned.

## Obtaining JWT Tokens

Vault expects a signed JWT token to verify against. There are a few ways to
acquire a JWT token.

### Generating IAM Tokens
### Generating IAM JWT

Vault includes a CLI helper for generating the signed JWT token and submitting
it to Vault for `iam`-type roles. If you want to generate the JWT token
yourself, follow this section.
This describes how to use the GCP IAM [API method][signjwt-method] directly
to generate the signed JWT with the claims that Vault expects. Note the CLI
does this process for you and is much easier, and that there is very little
reason to do this yourself.

#### Shell Example
#### curl

The expected format of the JWT request payload is:
Vault requires the following minimum claim set:

```javascript
```json
{
"sub": "$SERVICE_ACCOUNT",
"sub": "$SERVICE_ACCOUNT_EMAIL_OR_ID",
"aud": "vault/$ROLE",
"exp": "$EXPIRATION" // optional
"exp": "$EXPIRATION"
}
```

If specified, the expiration must be a
For the API method, expiration is optional and will default to an hour.
If specified, expiration must be a
[NumericDate](https://tools.ietf.org/html/rfc7519#section-2) value (seconds from
Epoch). This value must be before the max JWT expiration allowed for a role.
This defaults to 15 minutes and cannot be more than 1 hour.
Expand All @@ -257,8 +316,10 @@ curl \

#### gcloud Example

You can also do this through the (currently beta) gcloud command.

```text
$ gcloud beta iam service-accounts sign-jwt credentials.json - \
$ gcloud beta iam service-accounts sign-jwt $INPUT_JWT_CLAIMS $OUTPUT_JWT_FILE \
[email protected] \
--project=my-project
```
Expand Down Expand Up @@ -295,4 +356,5 @@ The GCP Auth Plugin has a full HTTP API. Please see the
[cloud-creds]: https://cloud.google.com/docs/authentication/production#providing_credentials_to_your_application
[service-accounts]: https://cloud.google.com/compute/docs/access/service-accounts
[api-docs]: /api/auth/gcp/index.html
[identity-group-aliases]: /api/secret/identity/group-alias.html
[instance-identity]: https://cloud.google.com/compute/docs/instances/verifying-instance-identity

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