better checking for security definitions (#11335)

Author: wing328

modules/openapi-generator/src/main/java/org/openapitools/codegen/DefaultCodegen.java

@@ -4849,10 +4849,13 @@ public List<CodegenSecurity> fromSecurity(Map<String, SecurityScheme> securitySc
                     // This scheme may have to be changed when it is officially registered with IANA.
                     cs.isHttpSignature = true;
                     once(LOGGER).warn("Security scheme 'HTTP signature' is a draft IETF RFC and subject to change.");
+                } else {
+                    once(LOGGER).warn("Unknown scheme `{}` found in the HTTP security definition.", securityScheme.getScheme());
                 }
                 codegenSecurities.add(cs);
             } else if (SecurityScheme.Type.OAUTH2.equals(securityScheme.getType())) {
                 final OAuthFlows flows = securityScheme.getFlows();
+                boolean isFlowEmpty = true;
                 if (securityScheme.getFlows() == null) {
                     throw new RuntimeException("missing oauth flow in " + key);
                 }
@@ -4862,28 +4865,38 @@ public List<CodegenSecurity> fromSecurity(Map<String, SecurityScheme> securitySc
                     cs.isPassword = true;
                     cs.flow = "password";
                     codegenSecurities.add(cs);
+                    isFlowEmpty = false;
                 }
                 if (flows.getImplicit() != null) {
                     final CodegenSecurity cs = defaultOauthCodegenSecurity(key, securityScheme);
                     setOauth2Info(cs, flows.getImplicit());
                     cs.isImplicit = true;
                     cs.flow = "implicit";
                     codegenSecurities.add(cs);
+                    isFlowEmpty = false;
                 }
                 if (flows.getClientCredentials() != null) {
                     final CodegenSecurity cs = defaultOauthCodegenSecurity(key, securityScheme);
                     setOauth2Info(cs, flows.getClientCredentials());
                     cs.isApplication = true;
                     cs.flow = "application";
                     codegenSecurities.add(cs);
+                    isFlowEmpty = false;
                 }
                 if (flows.getAuthorizationCode() != null) {
                     final CodegenSecurity cs = defaultOauthCodegenSecurity(key, securityScheme);
                     setOauth2Info(cs, flows.getAuthorizationCode());
                     cs.isCode = true;
                     cs.flow = "accessCode";
                     codegenSecurities.add(cs);
+                    isFlowEmpty = false;
+                }
+
+                if (isFlowEmpty) {
+                    once(LOGGER).error("Invalid flow definition defined in the security scheme: {}", flows);
                 }
+            } else {
+                once(LOGGER).error("Unknown type `{}` found in the security definition `{}`.", securityScheme.getType(), securityScheme.getName());
             }
         }