Failure messages for Group SAML

Description

We should consider creating informative failure messages for both:

• A group owner, configuring and testing a new/existing SAML connection for a group, and
• An individual user, attempting to auth into a SAML-connected group.

Proposal

Possible failure states we should build failure messages for:

Configuring/testing a new/existing SAML group:

• Bad URL
• Certificate error
• Attribute not mapped properly

User authing into the group:

• No connection/couldn't talk to the IdP
• Credentials not found on IdP
• Identity already associated with another group