Update KMS readme with vault quick start guide (#6747)

docs/kms/README.md

@@ -1,6 +1,6 @@
 # KMS Quickstart Guide [![Slack](https://slack.minio.io/slack?type=svg)](https://slack.minio.io)
 
-KMS feature allows you to use Vault to generate and manages keys which are used by the minio server to encrypt objects.This document explains how to configure Minio with Vault as KMS.
+KMS feature allows you to use Vault to generate and manage encryption keys for use by the minio server to encrypt objects. This document explains how to configure Minio with Vault as KMS.
 
 ## Get started
 
@@ -10,13 +10,49 @@ Install Minio - [Minio Quickstart Guide](https://docs.minio.io/docs/minio-quicks
 ### 2. Configure Vault
 Vault as Key Management System requires following to be configured in Vault
 
-- transit backend configured with a named encryption key-ring
-- AppRole based authentication with read/update policy for transit backend. In particular, read and update policy
-  are required for the generate data key endpoint and decrypt key endpoint.
+- [transit](https://www.vaultproject.io/docs/secrets/transit/index.html) backend configured with a named encryption key-ring
+- [AppRole](https://www.vaultproject.io/docs/auth/approle.html) based authentication with read/update policy for transit backend. In particular, read and update policy are required for the [Generate Data Key](https://www.vaultproject.io/api/secret/transit/index.html#generate-data-key) endpoint and [Decrypt Data](https://www.vaultproject.io/api/secret/transit/index.html#decrypt-data) endpoint.
+
+Here is a sample quick start for configuring vault with a transit backend and Approle with correct policy 
+#### 2.1 Start Vault server in dev mode
+In dev mode, Vault server runs in-memory and starts unsealed. Note that running Vault in dev mode is insecure and any data stored in the Vault is lost upon restart.
+```
+vault server -dev
+```
+
+#### 2.2 Set up vault transit backend and create an app role
+```
+cat > vaultpolicy.hcl <<EOF
+path "transit/datakey/plaintext/my-minio-key" { 
+  capabilities = [ "read", "update"]
+}
+path "transit/decrypt/my-minio-key" { 
+  capabilities = [ "read", "update"]
+}
+path "transit/encrypt/my-minio-key" { 
+  capabilities = [ "read", "update"]
+}
+
+EOF
+
+export VAULT_ADDR='http://127.0.0.1:8200'
+vault auth enable approle    # enable approle style auth
+vault secrets enable transit  # enable transit secrets engine
+vault write -f  transit/keys/my-minio-key  #define a encryption key-ring for the transit path
+vault policy write minio-policy ./vaultpolicy.hcl  #define a policy for AppRole to access transit path
+vault write auth/approle/role/my-role token_num_uses=0  secret_id_num_uses=0  period=60s # period indicates it is renewable if token is renewed before the period is over
+# define an AppRole
+vault write auth/approle/role/my-role policies=minio-policy # apply policy to role
+vault read auth/approle/role/my-role/role-id  # get Approle ID
+vault write -f auth/approle/role/my-role/secret-id
+
+```
+
+The AppRole ID, AppRole Secret Id, Vault endpoint and Vault key name can now be used to start minio server with Vault as KMS.
 
 ### 3. Environment variables
 
-You'll need the Vault endpoint, AppRole ID, AppRole SecretID, encryption key-ring name before starting Minio server with Vault as KMS
+You'll need the Vault endpoint, AppRole ID, AppRole SecretID and encryption key-ring name defined in step 2.2
 
 ```sh
 export MINIO_SSE_VAULT_APPROLE_ID=9b56cc08-8258-45d5-24a3-679876769126
@@ -26,14 +62,14 @@ export MINIO_SSE_VAULT_KEY_NAME=my-minio-key
 minio server ~/export
 ```
 
-Optionally set `MINIO_SSE_VAULT_CAPATH` is the path to a directory of PEM-encoded CA cert files to verify the Vault server SSL certificate.
+Optionally set `MINIO_SSE_VAULT_CAPATH` as the path to a directory of PEM-encoded CA cert files to verify the Vault server SSL certificate.
 ```
 export MINIO_SSE_VAULT_CAPATH=/home/user/custom-pems
 ```
 
 ### 4. Test your setup
 
-To test this setup, access the Minio server via browser or [`mc`](https://docs.minio.io/docs/minio-client-quickstart-guide). You’ll see the uploaded files are accessible from the all the Minio endpoints.
+To test this setup, start minio server with environment variables set in Step 3, and server is ready to handle SSE-S3 requests.
 
 # Explore Further