Reuse siwe authentication

[manumonti]

Type of PR:

• [ ] Bugfix
• [X] Feature
• [ ] Documentation
• [ ] Other

Required reviews:

• [ ] 1
• [ ] 2
• [x] 3

What this does: Add support to reuse SIWE messages on taco-web from other applications.

Issues fixed/closed:

• Fixes #...

Related to https://github.com/nucypher/sprints/issues/22

Why it's needed:

Explain how this PR fits in the greater context of the NuCypher Network. E.g., if this PR address a nucypher/productdev issue, let reviewers know!

Notes for reviewers: Based on #546 .

[derekpierre]

Related to https://github.com/nucypher/sprints/issues/22

[derekpierre]

Looking for reviews here.