Disable MIF authentication:
In Maximo 7.6.1 --> System property --> mxe.int.allowdefaultlogin = 1
This property also overrides the ALLOWDFLTLOGIN settings in the ejb-jar.xml file for the default integration user.
source: https://www.ibm.com/support/knowledgecenter/en/SSLKT6_7.6.1/com.ibm.mam.doc/overview/c_new_mif_sys_prop_.html
NOTE: Cluster environment, restart all the clusters.
Enable MIF authentication:
Maximo authentication is enabled by setting the mxe.useAppServerSecurity system property to 0 (false).
If maximo authentication is enabled, all HTTP-based inbound transactions must specify an HTTP header with the following attributes:
MAXAUTH
username:password (User credentials encoded to base64 format)
Note: I used this website to encode base64 https://www.base64encode.org/
Maximo Application Server authentication is enabled by setting mxe.useAppServerSecurity system property to 1 (true).
Take a backup of "ejb-jar.xml" from "maximo/applications/maximo/mboejb/ejbmodule/META-INF".
Modify "ejb-jar.xml" : ALLOWDFLTLOGIN as 1 (change 4 entries)
<env-entry>
<env-entry-name>ALLOWDFLTLOGIN</env-entry-name>
<env-entry-type>java.lang.String</env-entry-type>
<env-entry-value>1</env-entry-value>
</env-entry>
The ALLOWDFLTLOGIN value must be set to 1 (true) for each of the following services in the XML file:
Enterprise Services
Object Structure Service
Standard Services
Workflow service
Note: The default integration user is not supported if you use the REST API or OSLC API. After you update the ejb-jar.xml deployment file, you must rebuild and redeploy the Maximo EAR file.
Source: https://www-01.ibm.com/support/docview.wss?uid=swg21965724
Always try above steps in non production environments.