docs: fix security callbacks documentation for single vs multiple schemes

[devin-ai-integration]

Summary

Fixes the security callbacks documentation to correctly distinguish between single and multiple security scheme patterns. Previously, the documentation incorrectly showed the security callback pattern (returning a Security object) for single security schemes.

The key distinction:

• Single scheme: Use the scheme name directly as a property (e.g., bearerAuth) with a callback returning the credential string
• Multiple schemes: Use the security property with a callback returning a Security object to dynamically choose which auth method to use

Updates since last revision

Scaled back changes per user feedback - only TypeScript examples were updated. All other language examples (Python, Go, Java, C#, PHP, Ruby) were reverted to their original state since the user only provided TypeScript-specific feedback.

Review & Testing Checklist for Human

• Verify TypeScript single-scheme example is correct - Confirm that bearerAuth: async (): Promise<string> => { ... } is the correct pattern for single security schemes
• Verify TypeScript multiple-scheme example is correct - Confirm that security: async (): Promise<Security> => { ... } is the correct pattern for multiple security schemes
• Consider updating non-TypeScript examples - The non-TypeScript examples still show the old pattern (using security/securitySource even for single schemes). If the single-scheme pattern applies to other languages too, those examples may need separate updates.

Recommended test plan: Generate a TypeScript SDK with a single security scheme and verify the documented bearerAuth callback pattern works as shown.

Notes

• Requested by: ash@speakeasyapi.dev
• Link to Devin run: https://app.devin.ai/sessions/3826e8744a694c4988c822782eec267d

[devin-ai-integration]

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