Configure Vault with time-based, one-time passwords (TOTP) for MFA

Appropriate Vault Enterprise license required

This page demonstrates the TOTP MFA on ACL'd paths of Vault.

Configuration

Enable the appropriate auth method:
```
$ vault auth enable userpass
```

Fetch the mount accessor for the enabled auth method:

$ vault auth list -detailed

The response will look like:

Path         Type        Accessor                  Plugin    Default TTL    Max TTL    Replication    Description
----         ----        --------                  ------    -----------    -------    -----------    -----------
token/       token       auth_token_289703e9       n/a       system         system     replicated     token based credentials
userpass/    userpass    auth_userpass_54b8e339    n/a       system         system     replicated     n/a

Configure TOTP MFA:
Note: Consider the algorithms supported by your authenticator. For example, Google Authenticator for Android supports only SHA1 as the value of algorithm.
```
$ vault write sys/mfa/method/totp/my_totp \
    issuer=Vault \
    period=30 \
    key_size=30 \
    algorithm=SHA256 \
    digits=6
```

Create a policy that gives access to secret through the MFA method created above:

$ vault policy write totp-policy -<<EOF
path "secret/foo" {
  capabilities = ["read"]
  mfa_methods  = ["my_totp"]
}
EOF

Create a user. MFA works only for tokens that have identity information on them. Tokens created by logging in using auth methods will have the associated identity information. Create a user in the userpass auth method and authenticate against it:
```
$ vault write auth/userpass/users/testuser \
    password=testpassword \
    policies=totp-policy
```

Create a login token:

$ vault write auth/userpass/login/testuser \
    password=testpassword

Key                    Value
---                    -----
token                  70f97438-e174-c03c-40fe-6bcdc1028d6c
token_accessor         a91d97f4-1c7d-6af3-e4bf-971f74f9fab9
token_duration         768h
token_renewable        true
token_policies         [default totp-policy]
token_meta_username    "testuser"

Note that the CLI is not authenticated with the newly created token yet, we did not call vault login, instead we used the login API to simply return a token.

Fetch the entity ID from the token. The caller identity is represented by the entity_id property of the token:

$ vault token lookup 70f97438-e174-c03c-40fe-6bcdc1028d6c

Key                 Value
---                 -----
accessor            a91d97f4-1c7d-6af3-e4bf-971f74f9fab9
creation_time       1502245243
creation_ttl        2764800
display_name        userpass-testuser
entity_id           307d6c16-6f5c-4ae7-46a9-2d153ffcbc63
expire_time         2017-09-09T22:20:43.448543132-04:00
explicit_max_ttl    0
id                  70f97438-e174-c03c-40fe-6bcdc1028d6c
issue_time          2017-08-08T22:20:43.448543003-04:00
meta                map[username:testuser]
num_uses            0
orphan              true
path                auth/userpass/login/testuser
policies            [default totp-policy]
renewable           true
ttl                 2764623

Generate TOTP method attached to the entity. This should be distributed to the intended user to be able to generate TOTP passcode:
```
$ vault write sys/mfa/method/totp/my_totp/admin-generate \
    entity_id=307d6c16-6f5c-4ae7-46a9-2d153ffcbc63

Key        Value
---        -----
barcode    iVBORw0KGgoAAAANSUhEUgAAAM...
url        otpauth://totp/Vault:307d6c16-6f5c-4ae7-46a9-2d153ffcbc63?algo...
```
Either the base64 encoded png barcode or the url should be given to the end user. This barcode/url can be loaded into Google Authenticator or a similar TOTP tool to generate codes.

$ vault login 70f97438-e174-c03c-40fe-6bcdc1028d6c

Read the secret, specifying the mfa flag:

$ vault read -mfa my_totp:146378 secret/data/foo

Key                 Value
---                 -----
refresh_interval    768h
data                which can only be read after MFA validation