add vault's k8s authentication support

Dockerfile

@@ -0,0 +1,26 @@
+FROM golang:1.16 AS builder
+
+ENV GO111MODULE=on \
+  CGO_ENABLED=0 \
+  GOOS=linux \
+  GOARCH=amd64
+
+RUN mkdir /build
+WORKDIR /build
+
+COPY . .
+
+RUN go mod download
+RUN go build \
+        -a \
+        -trimpath \
+        -ldflags "-s -w -extldflags '-static'" \
+        -tags 'osusergo netgo static_build' \
+        -o ../vault_raft_snapshot_agent \
+        ./main.go
+
+FROM alpine
+WORKDIR /
+COPY --from=builder /vault_raft_snapshot_agent .
+COPY snapshot.json /etc/vault.d/snapshot.json
+ENTRYPOINT ["/vault_raft_snapshot_agent"]

README.md

@@ -61,12 +61,25 @@ If your configuration is right and Vault is running on the same host as the agen
 
 `frequency` How often to run the snapshot agent.  Examples: `30s`, `1h`.  See https://golang.org/pkg/time/#ParseDuration for a full list of valid time units.
 
+
+### Default authentication mode
 `role_id` Specifies the role_id used to call the Vault API.  See the authentication steps below.
 
 `secret_id` Specifies the secret_id used to call the Vault API.
 
 `approle` Specifies the approle name used to login.  Defaults to "approle".
 
+
+### Kubernetes authentication mode
+Incase we're running the application under kubernetes, we can use Vault's Kubernetes Auth
+as below. Read more on [kubernetes auth mode](https://www.vaultproject.io/docs/auth/kubernetes)
+
+`vault_auth_method` Set it to "k8s", otherwise, approle will be chosen
+
+`vault_auth_role` Specifies vault k8s auth role
+
+`vault_auth_path` Specifies vault k8s auth path
+
 ### Storage options
 
 Note that if you specify more than one storage option, *all* options will be written to.  For example, specifying `local_storage` and `aws_storage` will write to both locations.
@@ -118,6 +131,9 @@ Note that if you specify more than one storage option, *all* options will be wri
 
 ## Authentication
 
+
+### Default authentication mode
+
 You must do some quick initial setup prior to being able to use the Snapshot Agent.  This involves the following:
 
 `vault login` with an admin user.
@@ -143,3 +159,8 @@ and copy your secret and role ids, and place them into the snapshot file.  The s
 The AppRole allows the snapshot agent to automatically rotate tokens to avoid long-lived credentials.
 
 To learn more about AppRole's and why this project chose to use them, see [the Vault docs](https://www.vaultproject.io/docs/auth/approle)
+
+
+### Kubernetes authentication mode
+
+To Enable Kubernetes authentication mode, we should follow these steps from [the Vault docs](https://www.vaultproject.io/docs/auth/kubernetes#configuration)

config/config.go

@@ -11,16 +11,19 @@ import (
 
 // Configuration is the overall config object
 type Configuration struct {
-	Address   string      `json:"addr"`
-	Retain    int64       `json:"retain"`
-	Frequency string      `json:"frequency"`
-	AWS       S3Config    `json:"aws_storage"`
-	Local     LocalConfig `json:"local_storage"`
-	GCP       GCPConfig   `json:"google_storage"`
-	Azure     AzureConfig `json:"azure_storage"`
-	RoleID    string      `json:"role_id"`
-	SecretID  string      `json:"secret_id"`
-	Approle   string      `json:"approle"`
+	Address         string      `json:"addr"`
+	Retain          int64       `json:"retain"`
+	Frequency       string      `json:"frequency"`
+	AWS             S3Config    `json:"aws_storage"`
+	Local           LocalConfig `json:"local_storage"`
+	GCP             GCPConfig   `json:"google_storage"`
+	Azure           AzureConfig `json:"azure_storage"`
+	RoleID          string      `json:"role_id"`
+	SecretID        string      `json:"secret_id"`
+	Approle         string      `json:"approle"`
+	K8sAuthRole     string      `json:"k8s_auth_role,omitempty"`
+	K8sAuthPath     string      `json:"k8s_auth_path,omitempty"`
+	VaultAuthMethod string      `json:"vault_auth_method,omitempty"`
 }
 
 // AzureConfig is the configuration for Azure blob snapshots

main.go

@@ -46,15 +46,20 @@ func main() {
 
 	for {
 		if snapshotter.TokenExpiration.Before(time.Now()) {
-			snapshotter.SetClientTokenFromAppRole(c)
+			switch c.VaultAuthMethod {
+			case "k8s":
+				snapshotter.SetClientTokenFromK8sAuth(c)
+			default:
+				snapshotter.SetClientTokenFromAppRole(c)
+			}
 		}
 		leader, err := snapshotter.API.Sys().Leader()
 		if err != nil {
 			log.Println(err.Error())
 			log.Fatalln("Unable to determine leader instance.  The snapshot agent will only run on the leader node.  Are you running this daemon on a Vault instance?")
 		}
 		leaderIsSelf := leader.IsSelf
-		if ! leaderIsSelf {
+		if !leaderIsSelf {
 			log.Println("Not running on leader node, skipping.")
 		} else {
 			var snapshot bytes.Buffer

snapshot.json

@@ -0,0 +1,18 @@
+{
+   "addr":"http://vaul-addr:8200",
+   "retain":72,
+   "frequency":"3600s",
+   "role_id": "<vault app role id>",
+   "secret_id":"<vault app secret id",
+   "vault_auth_method": "",
+   "vault_auth_role": "",
+   "vault_auth_path": "",
+   "aws_storage":{
+      "access_key_id":"<s3 access id>",
+      "secret_access_key":"<s3 acess key>",
+      "s3_region":"<s3 region>",
+      "s3_bucket":"<s3 bucket",
+      "s3_endpoint":"<s3 endpoint>",
+      "s3_force_path_style":true
+   }
+}

snapshot_agent/agent.go

@@ -7,6 +7,7 @@ import (
 	"log"
 	"net/url"
 	"os"
+	"path"
 	"time"
 
 	"cloud.google.com/go/storage"
@@ -70,11 +71,10 @@ func (s *Snapshotter) ConfigureVaultClient(config *config.Configuration) error {
 		return err
 	}
 	s.API = api
-	err = s.SetClientTokenFromAppRole(config)
-	if err != nil {
-		return err
+	if config.VaultAuthMethod == "k8s" {
+		return s.SetClientTokenFromK8sAuth(config)
 	}
-	return nil
+	return s.SetClientTokenFromAppRole(config)
 }
 
 func (s *Snapshotter) SetClientTokenFromAppRole(config *config.Configuration) error {
@@ -86,7 +86,7 @@ func (s *Snapshotter) SetClientTokenFromAppRole(config *config.Configuration) er
 	if config.Approle != "" {
 		approle = config.Approle
 	}
-	resp, err := s.API.Logical().Write("auth/" + approle + "/login", data)
+	resp, err := s.API.Logical().Write("auth/"+approle+"/login", data)
 	if err != nil {
 		return fmt.Errorf("error logging into AppRole auth backend: %s", err)
 	}
@@ -95,6 +95,43 @@ func (s *Snapshotter) SetClientTokenFromAppRole(config *config.Configuration) er
 	return nil
 }
 
+func (s *Snapshotter) SetClientTokenFromK8sAuth(config *config.Configuration) error {
+
+	if config.K8sAuthPath == "" || config.K8sAuthRole == "" {
+		return errors.New("missing k8s auth definitions")
+	}
+
+	jwt, err := os.ReadFile("/var/run/secrets/kubernetes.io/serviceaccount/token")
+	if err != nil {
+		return err
+	}
+	data := map[string]string{
+		"role": config.K8sAuthRole,
+		"jwt":  string(jwt),
+	}
+
+	login := path.Clean("/v1/auth/" + config.K8sAuthPath + "/login")
+	req := s.API.NewRequest("POST", login)
+	req.SetJSONBody(data)
+
+	resp, err := s.API.RawRequest(req)
+	if err != nil {
+		return err
+	}
+	if respErr := resp.Error(); respErr != nil {
+		return respErr
+	}
+
+	var result vaultApi.Secret
+	if err := resp.DecodeJSON(&result); err != nil {
+		return err
+	}
+
+	s.API.SetToken(result.Auth.ClientToken)
+	s.TokenExpiration = time.Now().Add(time.Duration((time.Second * time.Duration(result.Auth.LeaseDuration)) / 2))
+	return nil
+}
+
 func (s *Snapshotter) ConfigureS3(config *config.Configuration) error {
 	awsConfig := &aws.Config{Region: aws.String(config.AWS.Region)}