OAuth validator modules are dynamically loaded from the shared libraries listed in oauth_validator_libraries. Modules are loaded on demand when requested from a login in progress. The normal library search path is used to locate the library. To provide the validator callbacks and to indicate that the library is an OAuth validator module a function named _PG_oauth_validator_module_init must be provided. The return value of the function must be a pointer to a struct of type OAuthValidatorCallbacks, which contains a magic number and pointers to the module's token validation functions. The returned pointer must be of server lifetime, which is typically achieved by defining it as a static const variable in global scope.

typedef struct OAuthValidatorCallbacks
{
    uint32        magic;            /* must be set to PG_OAUTH_VALIDATOR_MAGIC */

    ValidatorStartupCB startup_cb;
    ValidatorShutdownCB shutdown_cb;
    ValidatorValidateCB validate_cb;
} OAuthValidatorCallbacks;

typedef const OAuthValidatorCallbacks *(*OAuthValidatorModuleInit) (void);

Only the validate_cb callback is required, the others are optional.