If a message is not signed, the integrity the message cannot be guaranteed.
Any part of a message that is not signed has the potential to be intercepted and modified without being detected by the receiver. Without a signature, a receiver cannot cryptographically verify that the contents of a message are authentic.
The following service provider configuration tells Axis 2 to accept unsigned messages:
<service>
...
<parameter name="InflowSecurity">
<action>
<items>Timestamp Encrypt</items>
...
</action>
</parameter>
</service>
[1] Standards Mapping - OWASP Top 10 2004 - (OWASP 2004) A10 Insecure Configuration Management
[2] Standards Mapping - OWASP Top 10 2010 - (OWASP 2010) A6 Security Misconfiguration
[3] Standards Mapping - FIPS200 - (FISMA) CM
[4] Standards Mapping - Common Weakness Enumeration - (CWE) CWE ID 345
[5] Standards Mapping - Web Application Security Consortium 24 + 2 - (WASC 24 + 2) Insufficient Authentication
[6] Standards Mapping - Payment Card Industry Data Security Standard Version 1.1 - (PCI 1.1) Requirement 6.5.10
[7] Securing SOAP Messages with Rampart Apache Software Foundation