Ilmar Kerm

Oracle, databases, Linux and maybe more

Tag: pl/sql

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JSON Web Token (JWT) is a popular open standard that enables web applications to transfer information between parties asn JSON object. For example single-sign on authentication information. The information can be trusted, because the token also includes a signature. Verifying this signature is essential, otherwise anyone can fake the token contents.

Oracle APEX does provide APEX_JWT package, which handles the parsing and validity checking very well, but it can only verify the signature, if JWT was created using HS256 signature. HS256 is loosing popularity, since it is based on symmetric cryptography, meaning all parties must have access to the same encryption key.

Another, much more secure signature is now gaining popularity, based on RSA public key encryption – RS256. Here JWT is signed using a private key, but it can be verified using the corresponding public key. As the name suggests, public key is completely public and can be downloaded from the internet using kid attribute value present in JWT header (this service is called JWKS – JSON Web Key Sets). This is also the signature system AWS Cognito uses.

At the time of writing (APEX 23.1 and Oracle database 19.20), I did not find and ready code on the internet for verifying JWT RS256 signatures – so I had to create one. It lets APEX_JWT do the JWT parsing and validity checking, but I needed to add RS256 signature checking and downloading keys from JWKS store. It is intended to be used from APEX flows.

APEX_JWT_RS256 package repository can be found here

A quick example how to use the package as APEX page sentry function in custom authentication scheme.

create or replace FUNCTION JWT_PAGE_SENTRY RETURN BOOLEAN AS 
    v_required_group varchar2(30):= 'important_people'; -- Group needed to access the app
    v_iss varchar2(200):= 'https://cognito-idp.eu-central-1.amazonaws.com/eu-central-1_ZZxxZZxx11'; -- ISS that issued the JWT, YOU MUST CHANGE THIS to point to your own ISS
    jwt_cookie owa_cookie.cookie;
    v_jwt_payload varchar2(2000);
    v_jwt_json json_object_t;
    v_groups json_array_t;
    v_group_found boolean:= false;
BEGIN
    -- Do JWT token validation and check that correct group is granted to user
    -- 2023 Ilmar Kerm
    jwt_cookie:= owa_cookie.get('JWT_COOKIE_NAME');
    IF jwt_cookie.vals.COUNT = 0 THEN
        apex_debug.error('JWT session cookie not found');
        RETURN false;
    END IF;
    IF apex_jwt_rs256.decode_and_validate(jwt_cookie.vals(1), v_iss, v_jwt_payload) THEN
        -- JWT validated, now check the required group
        v_jwt_json:= json_object_t.parse(v_jwt_payload);
        v_groups:= v_jwt_json.get_array('cognito:groups');
        FOR i IN 0..v_groups.get_size - 1 LOOP
            IF v_groups.get_string(i) = v_required_group THEN
                v_group_found:= true;
                EXIT;
            END IF;
        END LOOP;
        IF NOT v_group_found THEN
            apex_debug.error('Required group is missing from JWT: '||v_required_group);
            RETURN false;
        END IF;
        IF v_jwt_json.get_string('token_use') != 'access' THEN
            apex_debug.error('Invalid value for JWT attribute token_use');
            RETURN false;
        END IF;
        IF V('APP_USER') IS NULL OR V('APP_USER') = 'nobody' OR V('APP_USER') != v_jwt_json.get_string('username') THEN
            APEX_CUSTOM_AUTH.DEFINE_USER_SESSION(
                p_user => v_jwt_json.get_string('username'),
                p_session_id => APEX_CUSTOM_AUTH.GET_NEXT_SESSION_ID
            );
        END IF;
        RETURN true;
    ELSE
        RETURN false;
    END IF;
END JWT_PAGE_SENTRY;

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I’ve been using InfluxDB for storing metrics, but it has hit its limitations – pretty huge memory consumption, so can’t really store some metrics for longer time and InfluxQL language itself is very limiting for analytics. So looking now into replacing it with Oracle 21c with JSON in-memory store and other goodies.

But InfluxDB has a nice GROUP BY time(<time interval>) clause that lets you group timestamps into arbitary length time groups – 1 minute, 2 minute, 5 minute, 15 minute, 3 hours…

In Oracle you can use built in TRUNC() or ROUND() to round timestamp into 1 MINUTE, 1 HOUR, 1 DAY, but not to 5 minute and so on.

Here are my functions to fix this issue.

Yes you are seeing correct, all TIMESTAMP data types. No DATE. Please stop using this old expired DATE data type. TIMESTAMPS are better as ISO joins are better 🙂

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I was looking for PL/SQL examples to use metadata and data filtering in datapump API, but I didn’t find any. So here is one example. It uses table reload_dev_tables to specify what schemas/tables should be exported using data pump and what where clause should be set.

Structure for reload_dev_tables:

 Name                                      Null?    Type                        
 ----------------------------------------- -------- -------------
 OWNER                                     NOT NULL VARCHAR2(40)                
 TABLE_NAME                                NOT NULL VARCHAR2(40)                
 IS_FULL                                   NOT NULL NUMBER(1)                   
 FILTER_PREDICATE                                   VARCHAR2(250)

Here is the datapump code itself, tested in 11.2.0.3. This is just a demonstration how to use the datapump API, specifically the metadata and data filters.

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Starting from 11.2 its possible to use SSL client certificates to authenticate yourself to a remote web service using SSL client certificates. I did not find much information on it using Google or documentation, that is why I’m writing this post.

Please refer to this post by Tim Hall to get started on connecting to HTTPS service using UTL_HTTP, all of this is needed before continuing with SSL client certificate authentication.

The first thing you need is to generate user certificate request inside Oracle Wallet, sign it by CA and load the returned certificate back to Wallet. I’m not going to very detailed steps here, but basically (using Oracle Wallet Manager OWM):

  1. Open the wallet you created using Tim Hall’s post mentioned previously.
  2. Go to Operations > Add Certificate Request
  3. Fill in all the needed fields
  4. After certificate request has been created, go to Operations > Export Certificate Request
  5. Send the request to a Certification Authority (that the remote service trusts) for signing and wait for a reply (in a form of signed certificate)
  6. Import the signed certificate to wallet – go to Operations > Import User Certificate

If you are using 11g OWM/ORAPKI and when importing the user certificate to wallet OWM displays an error or ORAPKI corrupts your wallet, you can just use OWM/ORAPKI programs from 10gR2 database client. This is due to bug Bug 9395937: UNABLE TO IMPORT USER CERTIFICATE IN OWM 11.1, WORKS IN 10.2.

Next thing is to add ACL privileges inside the database. UTL_HTTP documentation requires the use of use-client-certificates ACL privilege. How to do that I’ll refer to Tim Hall’s post again Fine-Grained Access to Network Services in Oracle Database 11g Release 1. In the example below I already have ACL all_access.xml and I’m granting connect and use-client-certificates privileges to CLTEST schema.

SQL> exec DBMS_NETWORK_ACL_ADMIN.ADD_PRIVILEGE('all_access.xml','CLTEST', true, 'connect');

PL/SQL procedure successfully completed.

SQL> exec DBMS_NETWORK_ACL_ADMIN.ADD_PRIVILEGE('all_access.xml','CLTEST', true, 'use-client-certificates');

PL/SQL procedure successfully completed.

Now the step that is not mentioned in UTL_HTTP documentation and got me stuck for weeks until I opened SR to Oracle Support. The network ACL needs also privileges on the Wallet file using DBMS_NETWORK_ACL_ADMIN.ASSIGN_WALLET_ACL.

SQL> exec DBMS_NETWORK_ACL_ADMIN.ASSIGN_WALLET_ACL('all_access.xml','file:/path/to/oracle/wallet');

PL/SQL procedure successfully completed.

After the privileges have been assigned, you can use UTL_HTTP to query remote web service like you do with normal HTTPS connection. If the remote web service requests client to be authenticated using certificates, UTL_HTTP automatically handles it in the background and uses the user certificate located in the wallet. For example:

SQL> SELECT utl_http.request('https://secure.service.com/status', '', 'file://path/to/oracle/wallet', 'WalletPassword') FROM dual;

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Oracle Database has had the possibility to run Java code inside the database for a long time. It’s a very rare occasion when you need to use it but still. Here is one example I used to download content from HTTPS website that required user certificates for authentication. Please take the code below more as an example how to put simple Java code inside the database, not as a solution for user certificates authentication, because UTL_HTTP can do the same thing (although I wasn’t successful in implementing it under 11.2.0.2).

First, load the Java source into database. The code below shows:

  • How to return simple datatype (int) from Java function – makeConnection
  • How to return Oracle CLOB datatype from Java – makeConnectionClob
  • How to execute SQL from Java, in the same calling session

Note that method main is just added for testing from command line.

Then you need to create a wrapper package in database. This declares the PL/SQL wrapper function names and input/output parameters.

Download the source: java_source.java and PL/SQL wrapper.sql.

When you first execute the code, you will most likely get some privilege errors, but the error message will tell you how to grant the needed privileges. For example, for this code the following grants were needed:

exec dbms_java.grant_permission( 'OWNER', 'SYS:java.util.PropertyPermission', 'javax.net.ssl.keyStore', 'write' );
exec dbms_java.grant_permission( 'OWNER', 'SYS:java.util.PropertyPermission', 'javax.net.ssl.trustStore', 'write' );
exec dbms_java.grant_permission( 'OWNER', 'SYS:java.util.PropertyPermission', 'javax.net.ssl.keyStorePassword', 'write' );
exec dbms_java.grant_permission( 'OWNER', 'SYS:java.net.SocketPermission', 'site.that.requires.user.cert', 'resolve' );
exec dbms_java.grant_permission( 'OWNER', 'SYS:java.net.SocketPermission', '1.2.3.4:443', 'connect,resolve' );

Ilmar Kerm