Spring Boot 2 Applications and OAuth 2: Setting Up an Authorization Server

This will be a 3 post series exploring ways to enable SSO with an OAuth2 provider for Spring Boot 2-based applications. I will cover the following in these posts:

1. Ways to bootstrap an OpenID Connect compliant OAuth2 Authorization Server/OpenID Provider.
2. Legacy Spring Boot/Spring 5 approach to integrating with an OAuth2 Authorization Server/OpenID Provider.
3. Newer Spring Boot 2/Spring 5 approach to integrating with an OAuth2 Authorization Server/OpenID Provider.

This post will cover ways to bootstrap an OpenID Connect compliant OAuth2 Authorization Server running on a local machine.

The post is essentially a rehash of an earlier post which went into the details of bootstrapping an OAuth2 authorization server using the excellent Cloud Foundry UAA project. There are a few changes since my previous post and I wanted to capture afresh the steps to bring up an Authorization server with a little more emphasis on changes to make it OpenID Connect compliant.

The best way to get a local version of a robust OAuth2 Authorization server running is to use the excellent Cloud Foundry UAA project.

Step 1: Clone the project:

git clone https://github.com/cloudfoundry/uaa

Step 2: Generate a keypair

UAA can make use of an asymmetric RSA keypair for signing and let clients verify the signature. I have a handy script available here which generates a keypair and generates a configuration file that can be used for bootstrapping UAA:

#!/bin/bash
openssl genrsa -out privkey.pem 2048
openssl rsa -pubout -in privkey.pem -out pubkey.pem

SIGNING_KEY=$(cat privkey.pem)
VERIFICATION_KEY=$(cat pubkey.pem)

JWT_SIGNING_KEYS=$(cat <<EOF
jwt:
   token:
      signing-key: |
$(echo "$SIGNING_KEY" | awk '{printf "       %s\n", $0}') 
      verification-key: |
$(echo "$VERIFICATION_KEY" | awk '{printf "       %s\n", $0}')
EOF
)

echo "$JWT_SIGNING_KEYS" > uaa_config.yml

rm privkey.pem
rm pubkey.pem

When run, this creates a UAA configuration which looks like this:

jwt:
   token:
      signing-key: |
       -----BEGIN RSA PRIVATE KEY-----
       MIIEpAIBAAKCAQEAuE5Ds...5Nka1vOTnjDgKIfsN
       NTAI25qNNCZOXXnGp71gMWsXcLFq4JDJTovL4/rzPIip/1xU0LjFSw==
       -----END RSA PRIVATE KEY-----
      verification-key: |
       -----BEGIN PUBLIC KEY-----
       MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAuE5DsCmjfvWArlCIOL6n
       ZwIDAQAB
       -----END PUBLIC KEY-----

Step 3: Use the configuration to start up the UAA server:

UAA_CONFIG_URL=file://$PWD/uaa_config.yml ./gradlew run

Step 4: Validate

A quick way to validate if the UAA has started up is to check the JWKS_URI, this is an endpoint which exposes the set of verification keys that a client can use to validate the token. For UAA, this is available at the "/token_keys" endpoint. This endpoint can be validated with either curl or httpie:

http GET http://localhost:8080/uaa/token_keys

# OR

curl http://localhost:8080/uaa/token_keys

If things are configured okay, an output of the following form is expected from this endpoint:

{
    "keys": [
        {
            "alg": "RS256",
            "e": "AQAB",
            "kid": "legacy-token-key",
            "kty": "RSA",
            "n": "APLeBV3dcUrWuVEXRyFzNaOTeKOLwFjscxbWFGofCkxrp3r0nRbBBb4ElG4qYzmbStg5o-zXAPCOu7Pqy2j4PtC3OxLHWnKsflNOEWTeXhLkPE0IptHPbc6zgVPP3EoiG_umpm0BYeJPZZc-7tA11uU_3NqidY9wnpOgKBuwNmdoyUrjb4fBDoMr_Wk2_sn_mtHSG8HaX8eJ9SbC9xRCJySjJDApOYR_dKjuwpbcM2ITfbTzD9M2J7yOtoJRkFhd1Ug2t_6AA_z47BBws-x9BBfSNbYGsVlDAbe6NK_jUE",
            "use": "sig",
            "value": "-----BEGIN PUBLIC KEY-----\nMIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEA8t4FXd1xSta5URdHIXM1\no5N4o4vAWOxzFtYUah8KTGunevSdFsEFvgSUbipjOZtK2Dmj7NcA8I67s+rLaPg+\n0Lc7Esdacqx+U04RZN5eEuQ8TQim0c9tzrOBU8/cSiIb+6ambQF62glGQWF3VSDa3/oAD/PjsEHCz7H0EF9I1tgaxWUMBt7o0r+N\nQQIDAQAB\n-----END PUBLIC KEY-----"
        }
    ]
}

Step 5: Populate Data

UAA has a companion CLI application called uaac, available here. Assuming that you have the uaac CLI downloaded and UAA started up at its default port of 8080, let us start by pointing the uaac to the UAA application:

uaac target http://localhost:8080/uaa

And log into it using one of the canned client credentials (admin/adminsecret):

uaac token client get admin -s adminsecret

Now that a client has logged in, the token can be explored using :

uaac token decode

This should display the details of the logged information in the client:

jti: 4457847692b7464ca0320f08271a9e98
  sub: admin
  authorities: clients.read clients.secret clients.write uaa.admin clients.admin scim.write scim.read
  scope: clients.read clients.secret clients.write uaa.admin clients.admin scim.write scim.read
  client_id: admin
  cid: admin
  azp: admin
  grant_type: client_credentials
  rev_sig: 3c12911
  iat: 1518332992
  exp: 1518376192
  iss: http://localhost:8080/uaa/oauth/token
  zid: uaa

The raw JWT token can be obtained using the following command:

uaac context

It will have an output which looks like this:

[3]*[http://localhost:8080/uaa]
  skip_ssl_validation: true

  [2]*[admin]
      client_id: admin
      access_token: eyJhbGciOiJSUzI1NiIsImtpZCI6ImxlZ2FjeS10b2tlbi1rZXkiLCJ0eXAiOiJKV1QifQ.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.ZEcUc4SvuwQYwdE0OeG5-l8Jh1HsP0JFI3aCob8A1zOcGOGjqso4j1-k_Lzm__pGZ702v4_CkoXOBXoqaaRbfVgJybBvOWbWsUZupMVMlEsyaR_j8DWY8utFAIiN2EsQgjG3qLrsf0K8lm0I3_UIEjaNZhSkWSLDLyY9wr_2SRanSf8LkcEJoSTTgDdO0aP8MvwNpDG7iQ2Om1HZEN08Bed1hHj6e1E277d9Kw7gutgCBht5GZDPFnI6Rjn0O5wimgrAa6FEDjdCpR7hy2P5RiOTcTvjj3rXtVJyVcQcxGKymZrY2WOx1mIEzEIAj8NYlw0TLuSVVOiNZ9fKlRiMpw
      token_type: bearer
      expires_in: 43199
      scope: clients.read clients.secret clients.write uaa.admin clients.admin scim.write scim.read
      jti: 4457847692b7464ca0320f08271a9e98

Finally, to add a client with credentials of client1/client1 and a user with credentials of user1/user1, use the following code:

uaac client add client1 \
   --name client1 \
   --scope resource.read,resource.write,openid \
   -s client1 \
   --authorized_grant_types authorization_code,refresh_token,client_credentials,password \
   --authorities uaa.resource \
   --redirect_uri http://localhost:8888/**


# Add a user called user1/user1
uaac user add user1 -p user1 --emails user1@user1.com


# Add two scopes resource.read, resource.write
uaac group add resource.read
uaac group add resource.write

# Assign user1 both resource.read, resource.write scopes..
uaac member add resource.read user1
uaac member add resource.write user1

At this point, we have a working Authorization Server with a sample client and a sample user available. The subsequent posts will make use of this data to enable authentication for a Sample Spring Boot2 application. I will update the links in this post as I complete the newer posts.