Glen Mazza's Weblog

I posted to Github a Spring Boot-based client library for making OAuth2-enabled REST calls to Salesforce's API. Supported are Salesforce's JWT Bearer Token and username/password flows discussed in my earlier blog post. The library supports use of Salesforce's REST API, SOQL Query, and Apex REST functionality. It uses Spring Security's OAuth 2 client to obtain access tokens necessary for making these calls.

The integrated test cases give examples of the client in action. As they involve creating, updating, and deleting Salesforce Accounts they should be run against a non-production instance. Salesforce offers free developer instances you can sign up for. Note the test case for the Apex REST functionality will require installing this Apex REST endpoint from the Salesforce documentation. To run the tests, first create an application-test.properties file in the itest resources folder with the configuration necessary for the flow you are using. There is a template file in that folder specifying what is needed for each OAuth2 flow type. For usage of this library by other applications, this configuration would be placed in the importing application's properties file. The library's SalesforceOAuth2Config class reads that configuration, and will halt on startup with informational messages if anything needed is missing. Once done, the integrated tests can be run from IntelliJ or command-line via ./gradlew integratedTest.

The Username/Password flow is supported out of the box by Spring, but the JWT bearer token flow requires some extra classes that I implemented following Spring's source code for their standard password and client grant flows:

• SalesforceJwtBearerOAuth2AuthorizedClientProvider - For each outgoing request to a resource server, checks if the JWT Bearer Token method is being used for access tokens and also if an authorized client (i.e., one with a valid access token) is already available. If yes and no, respectively, initiates the process to obtain a new access token to use with the resource API call.
• OAuth2SalesforceJwtBearerGrantRequest - created by above class, it holds the information necessary to create the JWT bearer token for making an access token request.
• OAuth2SalesforceJwtBearerGrantRequestEntityConverter - Constructs the JWT bearer token
• SalesforceJwtBearerTokenResponseClient - Uses the JWT Bearer token created by the above class to obtain a new access token from the authorization server.

Within the app, SOQL queries are handled by the SOQLQueryRunner which provides two options for responses: a JSON-formatted string or a developer-defined parameterized implementation of SOQLQueryResponse (example in the integrated test). The latter takes advantage of the fact that SOQL queries share much common structure and need only a relatively small portion to be overridden to hold fields specific to the SOQL query.

What happens when access tokens expire? The WebClient calls have a retry(1) setting that allows for one additional call to the resource server in case of an error such as using an expired access token. In such cases, for the first call, the failure handler in SalesforceOAuth2Config removes the authorized client instance (which has the invalid access token) from memory. For the retry call, SalesforceJwtBearerOAuth2AuthorizedClientProvider notes that there is not an authorized client instance anymore so proceeds to obtain a new access token to allow the second call to proceed. This functionality can be verified by revoking the access token from either Salesforce Setup's Session Management screen or from Connected Apps usage, and confirming that a subsequent resource API call still provides the data. Code breakpoints can also be used to confirm another access token was requested.

Additional Resources

• OAuth 2.0 Client - official Spring documentation
• Carey Development - Blog contains many useful tutorials, including on logging exceptions and reporting them to clients helpful for the creation of this client library.
• Spring WebClient – GET, PUT, POST, DELETE examples
• Spring 5 WebClient and WebTestClient Tutorial with Examples
• Salesforce Username/Password Flow Example - Very helpful in creating the Username-Password flow option in this library.